I think you're conflating the right to promote something abhorrent with permission to promote something abhorrent in my space. There are many examples of rights which can be exercised to perpetrate moral wrongs. Kickstarter isn't capable of impeding that. They are, however, well within _their_ rights to revoke access to _their_ mechanism.

Kickstater is, ultimately, a business, and they've decided they will make more money by doing a little of their own policing. If what's best for art isn't what's best for Kickstarter, expect them to do what's best for Kickstarter. If someone can compete with them by doing what's best for art instead, more power to them.