The betterment of the world as a whole?
"Since some people were confused when we funded Watsi, I'd better clarify that the money we're putting into the nonprofits will be a charitable donation, rather than an investment in the narrow sense. We won't have any financial interest in them."
Seen through that lens, it's straightforward to see how enabling people to come up with innovative and effective new charities that startup investors can help fund is a worthwhile project.