One of these things is not like the others. World peace is the obvious answer here.

World peace means no racism, it means more co-operation between people, and it means no money is being spent on war or arguably even law enforcement, meaning more money would go towards solving poverty and curing diseases.
World peace is the antidote to every single thing ailing this world.

I mean this is like asking, "What's the worst thing that can happen to you?"

1. Breaking your leg
2. Stubbing your toe
3. Being decapitated
4. Getting the flu

I choose Racism it's such a terrible problem

I really don't see it as a major problem as it once was and I live in Texas. The news resurfaced it again by completely misinforming people into un reasonable thoughts towards others. A lot of people, at least where Im from, don't discriminate based on color. The only place that I saw it as an actual problem is in Lousiana when I visited on a month long vacation. Of course, there is racism everywhere, but it has dramatically decreased from what it was in the late 1900's. And for poverty, well it's sad, but not everyone can remain above it. It just would not work economically. World peace would be great and would fix a majority of problems that are listed. All these factors would be great if achievable, but that will surely never be the case due to greed and power. Disease and cures for them are on the come up with technology and various advancements.

I would have to choose diseases because, hell who wants to get sick?