https://www.asstr.org/ the Alt Sex Stories Text Repository accepts erotic stories of any type or content. It has many such stories on file, dating back many years. It is most ly oriented to disply of stories, not to critical comment from readers. Caution, image on the opening page is Not-safe-for-work.
The ASSTR FAQ, under "Inappropriate Material" says:
One of ASSTR's founding principles is free speech, and as a result of this we welcome with open arms just about any kind of erotic literature that someone is willing to take the time to write. With this in mind, anyone with anything less than a completely open mind is sure to find something that would get their stomach churning or their temper flamed.
One thing to keep in mind is that most, if not all, stories at ASSTR are fictional. While something terrible, gross, and/or offensive may be described, remember that in all likelihood the event(s) never occurred in real life and in most cases the author is in no way advocating anyone taking part in such activities. Rather, some people enjoy writing about such events, and others enjoy reading them. We can't offer any further explanation than this.
As for the legality of some of the more offensive works at ASSTR, particularly those containing underage characters, the US Supreme Court ruled on April 16, 2002 that adult material depicting minors but that was not made through the use of any actual minor is protected free speech. The ruling was against the Child Pornography Prevention Act of 1996 (CPPA) and the entire ruling is available via Findlaw.com.
https://www.literotica.com/ is a somewhat similar site that includes a discussion board with a story feedback section A bit more restrictive on what content is accepted (for example no under-18 characters in a sexual relationship). Cover image is less prominent, but also not-safe-for-work.