I vote for ignorance, because so many other problems stem from it.
Originally Posted by Diego
What do you think is the biggest problem facing this world today?
Those are just some problems, you can choose any.
I think global warming is the biggest problem.
At least 3 of 4 of the problems you mentioned can be attributed to ignorance. (You can debate whether the problem of George Bush is caused by ignorance or not, or if he is a problem at all).
Oh, and by the way: AIDs and George Bush are not even close to being the biggest problems in the world.