This is absolutely false, at least in the US where Patreon is based. Out of curiosity where did you get the idea that insults are illegal (assuming you're talking about the Unites States)?
Calling someone a nazi when you cannot proof that they do indeed follow that ideology would also be slander/libel.
Someone tried to sue for calling someone a Nazi but lost [1]. In this case the defendant claimed to have been presenting a hypothetical. I have not been able to find a successful defamation case due to someone being called a Nazi in the US. Not to mention it wouldn't affect calling a black person a n____r because such a statement is not factually incorrect (as the slur is a derogatory term for a black person).
1. https://www.google.com/amp/s/www.thewrap.com/james-woods-bea...
Its just that coorporations are far more scared of beeing associated with the right, than the left.
Legally speaking you're not allowed to insult anyone, wether as a n-word, nor as a nazi