In the European Union, and I believe that in Canada and Australia as well (can't say for the USA), the law forbids any company or business to practice discrimination in consumers or employees treatment. They can't favor hiring a white person over a black person and they can't refuse to serve a homosexual consumer. Those are rights protected in the Constitution of those countries (for those who have one). No one can't be discriminated because of gender, race, religion, sexual preference.
That said, I can vouch that nowhere in the EU is a business obligated to provide a service or sell something that wasn't contractually agreed beforehand. Some companies that provide a community service (such as power company, water company, gas company, transports company, etc) are obligated to provide a product but that's because they are contractually obligated to do so, and they deliver a public service delegated by the government.
Private companies, like Patreon, or your local ice-cream provider, aren't obligated to deliver anything. They are obligated NOT to deliver prohibited services or goods, but they aren't obligated to deliver anything. The only obligation is towards their share-holders, not the community, not the law.
Now, I'll suppose California laws function similarly, and Patreon has the liberty to allow creators to use its platform to promote anything it wants, to the extent that it's not a law-prohibited content. If it's legal content (such as Incest might be under Californian law or Federal law, I don't know), Patreon reserves to itself the right to arbitrary decide to allow it or not and no court of law has the power to decide otherwise.
The matter would be entirely different, and more complex, if Patreon decided to ban homosexual non-sexual content, like a gay person's blog about his life or something like that. If Patreon allowed heterosexual people to blog about their life but banned a homosexual blog that would be discrimination, and therefore an illegal treatment, eligible for court action. Despite that, if Patreon decided to ban ALL life blogs then it wouldn't be discrimination at all and that wouldn't be eligible to a court action.
Shark doesn't have legal substance to sue the store for his favorite ice-cream, I'm afraid. Unless he could prove that the store did that to avoid Shark, specifically, to set foot in the store, and therefore, practicing an indirect discrimination... and that would be a very long shot, without just cause in my opinion, because such discrimination would be based on Shark's volition. He could still enter the store and buy other ice-creams, and the store couldn't do anything about it.
Likewise, Patreon isn't banning anyone from its services. The webcam sexy host that depended on Patreon for her income wasn't banned from the site; her content was. She can always open a new page about a webcam hostess blog and try to make income from that.
Patreon has open arms to any creator who wants to do art. Patreon won't just accept any kind of art, because, let's face it, the concept of art has been perverted and abused for the sake of easy income. A webcam masturbation show for the 20$ tier patrons isn't - not to my sensibility - properly art.
It seems to me that Patreon didn't anticipated the abusive behaviors, and that was their sin. It may not have had guidelines about forbidding Incest from the start but it sure has always said, from the beginning, that it wasn't a pornography friendly platform. There no doubt about it.