I'm back. Right so this question.. A lot of people bring up, and it frustrates me because... I feel like it's been answered a lot.
I'm not gonna ask you to watch the entire thing, but this is an excellent uh.. Mannerism to explain the reasoning (big words, heh). Like the person above me said, it's about Free Will. The idea that things like love, and happiness are meaningless if you forced whatever you created into that fashion. I think anyone can agree with that.
If you're a parent, and you force your children to say "I love you", and you force your children to do x, y, and z.. How do you know it comes from their heart? You don't. So, yes, God, in the Christian/Catholic sense, has the ability to stop all suffering and if He wanted to, He could obliterate Satan right now, but the reason He let events transpire the way they did was out of love for everything He created. Love that essentially means that.. "I love you so much, I want you to do whatever you want to".
The ideas of suffering, sin and death are caused directly because of Satan, and more so because of the rejection of God by humans. You can read more into how this all plays out, but that's essentially the reason behind that.. Why is there suffering.. Story.
I don't personally like it. I'd prefer to.. Y'know.. Not have been created at all. If not that, then I don't know why everyone has to suffer because of what two people did, supposedly. Which doesn't make sense because.. I believe in Darwinism and.. Yeah, it's messy.