I've Never Understood Why the "Problem with Evil" is Supposed to be the Toughest Question for Religion

First of all, of course if humans have free will - or even the illusion of free will - they will sometimes do bad things.

But it's not just for the sake of free will. We should want a universe in which bad things happen. How else would we know joy, but by knowing sorrow? Excitement but by boredom?

John Polkinghorne:

"We all tend to feel of course that if we'd been in charge of creation we'd have done it better. We'd have kept all the nice things and thrown away all the nasty things, but the more science helps us to understand how the world actually works, the more we see that these things are inextricably entangled with each other. You can't pull them apart. Here's the good things - keep those. Here's the bad things - don't keep those.
So the fact of cancer in the world is not gratuitous. It's not due to God being callous or incompetent in some sort of way. It's the inescapable shadow side of a creation which creatures make themselves."

Just think, if you never knew thirst, you'd never know taking a drink of cold water when you were thirsty. If you never knew sickness, you'd never know how much better it feels to get better, or the beauty of the compassion and sacrifice of those who care for the sick, the dying. You wouldn't appreciate warmth if you were never cold, kindness if no one was ever mean, peace without war, Holocaust jokes without... er, forget that one.

Brene Brown:

“The problem is [...] that you cannot selectively numb emotion. You can't say, 'Here's the bad stuff: here's vulnerability, here's grief, here's shame, here's fear, here's disappointment, I don't want to feel these. I'm going to have a couple of beers and a banana nut muffin. I don't want to feel these.' [...]

You can't numb those hard feelings without numbing the other affects or emotions. You cannot selectively numb. So when we numb those, we numb joy. We numb gratitude. We numb happiness. And then we are miserable, and we are looking for purpose and meaning, and then we feel vulnerable, so then we have a couple of beers and a banana nut muffin. And it becomes this dangerous cycle."

Preach it!

Alan Watts:

"Nobody ever saw crests without troughs or troughs without crests, just as you don’t encounter, in life, people with fronts but no backs; just as you don’t encounter a coin that has a heads but no tails. And although the heads and the tails, the fronts and the backs, the positives and the negatives are different, they’re at the same time one. And one has to get used fundamentally to the notion that different things can be inseparable That what is explicitly two can at the same time be implicitly one. If you forget that, very funny things happen.

If we, therefore, forget, you see, that black and white are inseparable, and that existence is constituted equivalently by being and non-being, then we get scared, and we have to play a game called, “Oh-oh, Black Might Win.” And once we get into the fear that Black, the negative side, might win, we are compelled to play the game, “But White Must Win.” And from that start all our troubles...

So a game with good and evil equally balanced isn't a good game. A game with the positive or good forces clearly triumphant isn't an interesting game. What we want is a game where it always seems that the good side is about to lose, in really serious danger of losing."