I agree in principle, but I have basically no confidence in my ability to figure out what to do to help people in the future. There are two obstacles: random error and bias. Random error, because predicting the future is hard. And bias, because any policy I decide I like could be justified as being good for the future people, and that assertion couldn't be refuted easily. The promise of helping even an enormous number of people in the future amounts to Pascal's Wager, where donating to this or that charity or working on this or that research is like choosing this or that religion; all the possibilities cancel out and I have no reliable guide to what to actually do.

Admittedly this is all "I failed my art" stuff rather than the other way around, but well, it's still true.