I don't think libertarians believe they should keep 100% of their income, in an ancap world a big chunk of their money would go to private competing institution

I don't think libertarians believe they should keep 100% of their income, in an ancap world a big chunk of their money would go to private competing institutions and charities. In fact some of the biggest donors to charities (and tax payers) tend to be libertarians. Also, let's not kid ourselves, we're all selfish. That being said, not saying an ancap world would be heaven on earth, not that what we have right now is either.