Values and principles are largely subjective. It's only through overwhelming, collective agreement that some things become so valuable as to be declared human rights, even when it's staunchly evident they are, e.g. the rights of LGBT people.

I think a lot more political debate similar to this has been voiced and argued about parentless adults being required to pay taxes to support schools. While I think one could easily argue that public schooling is a greater good all must contribute to in order to better society, (though I could easily find you people who would vehemently disagree for some cockamamie reason) there simply isn't that sort of collective thinking about veganism.