So you shouldn't have to provide services to people you find objectionable, even if those people are in a protected class? It's a common but mistaken belief that we have no obligations to society or to our fellow citizens.
For hosting specifically, it depends on multiple factors: your ubiquity, the demographics of your audience, the intended/stated purpose, etc. For instance, the Supreme Court recently decided unanimously that social media is the public square, and so no law can restrict access to social media (they were trying to ban sex offenders from social media).
Considering Twitter's and Facebook's stated purposes are to become the place for all online conversation and debate, if they achieve that goal then censoring content arguably violates people's rights. Doubly so because people like Jack Conte have literally stated that access to social media is a human right.
In this case, the Supreme Court made it clear that governments cannot prevent people from using social media. However other Supreme Court decisions have it that property owners don't have to allow others to use their property for speech, except in unusual cases like company towns.
It's not obvious to me that they will find these two ideas to be in conflict.