I think that this is a perennial question here. It is always in the background and at times when an incident pushes lots of emotional buttons it boils over into a major meta upheaval. There are various claims and contentions that certain content and topics are simply not acceptable on what is supposed to be a progressive web site. That probably is true. The question is where should these limits be drawn. That is not so easy to answer.
The ultimate hard line is when Marcos occasionally draws one. The only one of those that seems clearly fixed to me is the conspiracy theory issue. The other incidents that he has made a point of calling out seem to about a matter of degree. The practical reality is that this is a community moderated site. It is up to The Community to determine what is and is not acceptable.
There are general guidelines. Most of those have to do with limits on the style of expression rather than specific content. This is supposed to be a site for debate of issues. People who write diaries cannot prohibit people from expressing opinions that simply disagree with their opinions. The only official exception to this is the IGTNT diaries.
There is a range of content which has reached the level of a fairly general consensus that it is unacceptable. On issues like racism, sexism and homophobia there is a sense of where things cross a line. The way that this line gets demonstrated is when diaries or comments get a significant number of HRs. If they get enough of them, the user gets a timeout or get banned. That is how community moderation works here. An operational definition of what is unacceptable is that which gets HRed.
We have other instances where there is an extensive difference of opinion about the appropriateness of discussion. For the most part that is what is going on right now with the debates over gender issues and diary titles. There is lots of disagreement but very little use of HRs. There isn't sufficient consensus on the issues to generate a concerted movement of community moderation. So, we have debate.
The people claiming that certain topics and issues should simply be off limits for disagreement and debate are entitled to express that opinion, but clearly the reality is that a lot of other people don't agree with that. What people do seem to agree with is that the discussion and debate ought to be conducted without resorting to personal abuse and insults. So it appears to me that simply declaring a subject off limits for debate doesn't make it so. You have to persuade a majority of people to agree with you.