Yes, this is what I was alluding to. Freedom of expression was essential for the fight against racial segregation in the US. And for the fight for homosexual rights.
And yes, it's true that the Constitution only applies to government action. So private individuals have more freedom to discriminate and censor. Those rights are generally limited, however, for those who provide public services.
For example, if you're seeking a housemate, or inviting people over for dinner, you're free to discriminate. Even over protected categories, such as race, religion and gender status.
But if you're renting or selling an apartment or house, or running a restaurant, you are far less free to discriminate. In particular, over those protected categories. Indeed, you will be required to accommodate needs of those with differing abilities.
The relationship of discrimination and censorship is admittedly complex. In most of the US, for example, shopping malls cannot legally discriminate against protected classes. However, they can freely censor speech. And exclude people who say or do stuff that's against their rules.
Given all that, Patreon is indeed free to censor and exclude. Just as shopping malls are (except, as I recall in California). But even so, there is the expectation that operations that are effectively public spaces (even though they are not governmental) ought to respect rights to free expression. That was typically so for newspapers. And there's been considerable litigation over protests in shopping malls.
So can Patreon legally discriminate and censor, based on politics? Yes, clearly. But can they legitimately be criticized for doing so? Also yes.