Problems with non-diversification:

1. How do you choose between multiple things that are all necessary when leaving out one of them means disaster? For instance clean air v.s. clean water. Humanity needs both, or it dies. There must be more than one charity that's necessary.

2. How do you choose between multiple risks when any of them can kill you and they're equally likely? For instance: According to a TED video, there's around a 1 in 20,000 chance of a meteor hitting earth and according to some research I did a long time ago, the chance that Yellowstone caldera will erupt in our lifetimes and destroy earth is about 1 in 20,000.

3. If all of your favorite charities are likely to make their donation goals, why not donate to them all?

4. Sometimes one cause is dependent on another. For instance, how many charity websites are hosted on Linux / Apache - open source software. If Linux were in desperate need of programmers to solve some security flaw, it might make more sense to donate for that than to the charities that require them.