I don't buy any of this 'we are fallen' stuff. I do however believe that God has a different viewpoint to us. One we cannot ever really hope to understand. When someone we love dies we are wounded beyond belief but how do we know that the person who died isn't better off/happier or whatever. It may not make us happy to lose them or to believe they could possibly be better off but we can't see the whole picture.
Also who is to say that the unhappiness we deal with now does not by our efforts to bear it give us an eternity of happiness/contentment later - We just don't know.
If we believe in God we have to trust that what happens to us in this life is but an instant compared to what will happen when we join him/her. When our toddler screams in agony when you take his favourite toy off him he only understands you have taken something he loves, not the reason that you have taken it from him and there may be a good reason from your point of view - but that will take into account the bigger long-term picture.
This does not however negate the fact that we have a responsibility to try and alleviate suffering wherever we see it, without having the opportunity to do that we are unable to progress spiritually. To do this we need the suffering to exist. Not eating chocolate cake means nothing if it doesn't exist, it has to be there in order for us to feel virtuous at having resisted it.
I do not however think that this is reasoning you should use with someone who has been bereaved. It would be crass as they are in pain and just need sympathy and understanding not to have some 'theory' spouted at them. After all it is just a theory.
If someone who has been bereaved askes me this I say. I don't know why he allows things to happen, but for me the thought he exists helps me to cope with things. If it helped me to cope to believe he doesn't exist then I probably wouldn't believe in him.
One thing I would add is that the fact that someone is angry with God probably means they still believe in him even if they say they don't. How can you be angry with something you don't believe exists?
If we don't believe in God this is all of course a crock of s*t and I can understand that viewpoint too - it is just too bleak a viewpoint for me to have.