If I didn't care about other people, I wouldn't worry about donating to charities that actually help people. I'd donate a little to charities that make me look good, and if I'm feeling guilty and distracting myself doesn't seem to be cost-effective, I'd donate to charities that make me feel good. I would still keep quite a bit of my money for myself, or at least work less.

As it is, I've figured that other people matter, and some of them are a lot cheaper to make happy than me, so I decided that I'm going to donate pretty much everything I can to the best charity I can find.