The problem that I see with the whole "one needs coldness in order to appreciate warmth" idea is that I don't think it's actually true. To take the most obvious example, do people who live in Hawaii their whole lives deal with the same discomfort that people who live in Siberia their whole lives must deal with? I don't think they do. I think Hawaiians can easily appreciate their own weather without having to know what it feels like in Siberia. And I think the same can be said for any other example that this coldness/warmth analogy can be used for. (For example, I don't first need to be paraplegic in order to enjoy my ability to move around and not be confined to a wheelchair).
Now, it might be true that a Siberian would be able to enjoy an average day in Hawaii better than a Hawaiian would (or that a paraplegic who suddenly gained the ability to move his limbs would enjoy it more so than those of us who sometimes take such luxuries for granted would), but I hardly think that this increase in happiness would be enough to outweigh all the cold days (or paralysis) one would need to endure in order to achieve it. And honestly, I have my doubts that this would even be the case at all. It seems to me that bad days and sadness damage people and make it even more difficult for them to enjoy the good days than they would have been able to had they just had normal lives.
Even if humans are constructed in such a way that we can't be happy all the time (which i don't think is actually the case), does that really mean that that's any sort of "law of the universe"? wouldn't it really just be a part of being human? In other words, just because people DO tend to become complacent with good things and sometimes need a bad experience to get them to appreciate how good they've got it, why is that any sort of a mindset that a god would NEED to include in people in order to keep from disobeying the laws of logic? If a god had made his people able to be happy all the time, without ever requiring sadness to compare it to, then would that god really be in any sort of violation of the physical laws of the universe? I don't see how (though, if your answer has something to do with freewill, I'm getting to that). And of course, that doesn't even begin to touch up on the question of,,, How omnipotent could a god really be if he has to follow laws of physics and logic anyway? Such a god would clearly be one who had no say in what the laws of the universe would be. Not much of a god at all, truth be told.
And so the question still remains, why would a god have instilled this duality in us, making it impossible for us to be happy on a consistent basis?
Before we delve into possible reasons for why god would have "had" to have done this, let's look at the implications of this. Will it be just as impossible for people to have perfect, continuously happy lives once they're in heaven? Or will they be able to appreciate heaven fully simply because they've already experienced imperfection while here on earth? And if this is the case, then what does that say about aborted fetuses and miscarried babies who go straight to heaven without ever even being able to experience a bad day? (And if you're thinking that being vacuumed out of a womb is traumatic, then know that it is not until the third week of development that anything remotely nerve-like appears, and so quite factually speaking, it would be impossible for such an embryo ever to be able to feel pain or have bad thoughts, despite what sort of a "soul" they might already be in possession of.)
Would these aborted and miscarried individuals not be able to enjoy heaven as much as everyone else there simply because they have no concept of badness? If so, then that's a markedly unfair thing to allow to happen (even for the god of the bible). I have trouble believing though that anyone would maintain such a position. But if it's not the case, then HOW will such individuals be able to experience happiness without first knowing sadness, and WHY isn't this something possible for the rest of us? --- Let me rephrase that last bit just to make my point clear. If aborted babies ARE IN FACT able to appreciate heaven to the full extent that everyone else is, despite their never having experienced anything bad, then that invalidates the idea that people can only experience perfection if they first know imperfection. In other words, the idea that fetuses enjoy heaven as much as other people do CONTRADICTS the idea that one must first know pain in order to experience joy. You cannot believe both.
Let's now leave behind the notion that one needs bad in order to appreciate good, since it's been pretty much entirely dismantled, and let's move on to the notion of freewill.
There are two ways in which freewill can be used to argue for why a god would allow evil to occur. One argument is that we can't be happy unless we have the freedom to make choices. Is this really true though? In many cases it's important to be able to choose between things because that's what allows us to get what we want. But if we only have one option, and it just so happens to be what we want, then isn't that all we need?
To illustrate this, allow me to propose the following hypothetical. Imagine that you're headed toward an ice cream store and are desperately craving banana ice cream. You've been to this store before, and you know that they offer three flavors (coconut and lime being the other two flavors). Upon arriving though, you learn that there was an inordinate amount of business done that day and that the store has run out of most of its ice cream. Now, without my revealing to you which flavors the store still has left in stock, ask yourself, which of the following two situations would you prefer (keeping in mind that banana ice cream is the flavor you most desire)?
Situation A, in which banana has run out but you can still choose between coconut and lime? or Situation B, in which only banana is left? --- Doesn't situation B seem like the more preferable situation of the two even though you're not able to choose between more than one flavor?
This example might sound ridiculous because it's rare that things work out this way, but it's not ridiculous when we consider the idea of a god who can create individuals in any way that he pleases and who wishes them to live fulfilled lives. Imagine if we were to create an artificial intelligence, and instead of installing in it a program that allowed it to do whatever, we programmed it to behave in a very precise and specific manner. But imagine that we also equipped it with the ability to enjoy its existence 100% of the time. Would this really be such a mean thing to do? Provided that the happiness of this artificial intelligence didn't get in the way of its survival or the happiness of others, then I don't see how it could be.
For some of you though, the idea might still seem a little weird., the idea of a god who creates beings to sit around and enjoy things all day without ever having to choose anything. You might feel that a lack of being able to make choices (even if what you wanted always came to you without your ever having to choose it) would somehow prevent one from ever being able to feel truly comfortable. And while there are so many facets of this topic that we could explore, I'd like to focus on just one. If the idea of a god who creates people without the ability to choose makes you uneasy, then ask yourself if this isn't exactly what you believe in. Because if you believe that god made everything and that god knows everything, then is freewill even a possibility?
Every day, everything you do is something that your god knew would happen, whether it's what clothing you decide to where or where you end up when you die. So even if you are the one in control of your choices, there's still no variation. You were ALWAYS going to choose coke over pepsi, or paper over plastic. There was never a "maybe" about what would happen., at least not for your god. There might have been a "maybe" for you, but only because you can't see your own future (which is set - it must be if your god knows that something definitely WILL or WON'T happen), not because there's any sort of actual possibility that things could happen any other way.
And if it doesn't bother you that everything is set and either will happen or won't, then further consider that every faculty you use to make decisions is a part of a brain that was made not by you, but by your god. When you choose what you want on your pizza or what color to paint your bathroom, are you really choosing? Or are you simply obeying your taste buds and the parts of your brain where preferences are stored? And if that's what you're doing, then how can you not be said to be an automaton programed by a god, with no actual freewill? -- Simply put, in a godless universe, it's conceivable that individuals might make their own decisions, whatever exactly that means, but there's really no room for it in a universe where everything was made by a god.
The other way in which freewill can be used to argue for god's allowing evil to exist is one that occupies a much more base level of reasoning. It basically states that if god prevented evil, that he would be taking away man's freedom to sin (and by consequence, hurt others and run the risk of landing himself in hell), and that this would somehow be an immoral thing for a god to do.
There are a number of problems with this argument though. For one thing, it only explains actions done by other people. It doesn't explain things like natural disasters and diseases. Things like earthquakes (and presumably viruses) don't practice freewill and can't be offended by being restricted from carrying out certain actions, and so this argument does nothing to explain why a god would allow millions of people every year to be killed by floods, malaria, car accidents, or falling off of balconies. For another thing, if it's so immoral not to allow people to go around raping and killing, then are police officers being immoral when they try to prevent such acts? Are we going against god by insisting that thieves and murderers not be allowed to do what they want, or to put it another way, execute their freewill? Moreover, can god even be credited with always upholding this idea that it's wrong for him to restrict people's freedom to harm others? Surely he intervenes some of the time, allowing good to triumph over evil. But does that mean then that in these examples god is guilty of restricting the bad guy's freedom?
Yet another problem with this argument is that we're already so restricted anyway. If we DO have freewill, we don't have much of it. We can't, for example, choose to grow wings and fly around, or shapeshift or explore other dimensions. We're very limited. So if freedom is so important and integral to our happiness, then why are there so many things that god simply does not give us the freedom to do? And what harm would it really have done for him just to go the extra step and take away man's ability to kill? Denying man the ability to fly but then granting him the ability to kill people seems like somewhat of a design flaw to me.
My biggest problem though with the whole "god allows person A to harm person B because it would be immoral for god to control what person A does" idea, as if there aren't already enough problems with it, is that it focuses only on what's good for person A and neglects what's good for person B. In order for a god to be moral, he needs to do more than just allow people to do what they want., He also needs to protect people. And in a situation where god sits back and watches as a serial killer cuts a victim into little pieces or a leader of a nation genocides some minority group, then I'd say he's failing to carry out his moral obligation to protect the victims of these crimes. What this would boil down to, if any of it were actually true, is that god is more concerned with being moral to murderers than to the victims that those murderers harm. And how can that be said to be moral, to prioritize one person's freedom to harm over another person's freedom NOT to be harmed? The answer is, it can't be. It's just a poorly thought through excuse that people use to try to reconcile the idea that there's a loving god who can guarantee that everything will work out with the reality that clearly no such god actually exists.