TLDR: (Using Phil Libin's own logic against him) Startups are likely to fail, so it's just as absurd to say you're doing it to change the world as it is to believe you're doing it for the money. You're still better off joining an organization that has momentum and resources.

This invites inevitable argument though, since: 1. It's endlessly debatable which companies are actually changing the world. 2. The ones most people think of first are based on charity, which is again arguable and limited to very short term gain.