> fighting authoritarianism, inequality, genocide. Are these too boring?

Right, have the tech guys spent their money on politics - that seems to be working out well.

> fighting starvation

We have enough food in the world: we don't choose to share it or distribute it. Politics.

> fighting disease

Politicised within the US (measles, birdflu, NHI, health insurance), and similarly politicised within my own country (US social media is only partly to blame).

Bill Gates put a lot of money towards helping fight Malaria and other health issues: I would guess no other rich dudes wish to get similarly tarred.