The euphemism treadmill is basically arbitrary most of the time. For example, "people of color" is very PC right now, but "colored people" is considered KKK-language. It is what it is.

Also black people is a kind of strange term. Pretty much all black people are okay with it, but a lot of white people are weirdly afraid of saying it, especially in formal settings.

Language can be pretty arbitrary. It's not as though science fiction reliably has any science in it, even fake science.

Isn't a similar dynamic involved anywhere where people are developing an idea that offensively contradicts the belief of a majority?

This looks like begging the question to me. Whether an idea offensively contradicts mainstream beliefs has a lot to do with the connotations that happen to be associated with it. Lots of reasonably popular ideas contradict mainstream beliefs, but are not especially offensive. Obviously, once an idea becomes popular enough to be part of the mainstream, this whole distinction no longer makes sense.

We could similarly ask why are some atheists so agressive, and whether it wouldn't be better for others to avoid using the "atheist" label to avoid the association with these people ...

Indeed, this explains why many non-theistic people steadfastly refuse to self-identify as atheists (some of them may call themselves agnostics or non-believers). It also partially explains why the movements "Atheism Plus" and "Atheism 2.0" have started gaining currency.

Similarly, any useful and non-offensive content of "red pill" beliefs may be easily found and developed under other labels, such as "seduction community", "game"/"PUA", "ev psych" and the like.

Therefore the most famous writers of non-mainstream opinions will be the shocking ones.

It's not clear why we should care whether a writer of non-mainstream opinions is famous especially when such fame correlates poorly with truth-seeking and/or the opinions are gratuitously made socially unpopular for the sake of "controversy".

There are words which have both positive and negative connotations to different people.

Serious question, name a positive connotation of "The Red Pill" - which is not shared by "Game"/"PUA"/"seduction community" or "ev psych".

I'm not necessarily disagreeing that the red pill writers are pursuing an effective strategy in disseminating their beliefs. To be honest, I can see it either way. On the one hand, offending people gets them to notice you, and emotionally charged arguments are more interesting. On the other hand, some of the rhetoric might needlessly alienate people, and to a certain extent it can discredit the ideas (e.g. someone recommends Athol Kay, someone says "isn't he one of those red pill guys? I saw Roissy's blog and it was appalling, no way I can listen to one of them"). I definitely don't think that being deliberately offensive is literally the only way to spread a contrarian belief.

But I don't think the red pill movement should be able to have their cake and eat it too. You can't deliberately make your writing as offensive and obnoxious as possible in order to try to get it to spread, and then turn around and say "People are offended? This just shows that anyone who doesn't think like the mainstream becomes a public enemy!"

Mencius Moldbug

This is beside the point, IMHO; Moldbug's references to "taking the red pill" are well explained by his peculiar writing style. I think they are mostly unrelated to how Athol Kay, reddit!TheRedPill and others use the term. OTOH, Multiheaded's comment upthread provides proof that Kay's views are genuinely problematic, in a way that's closely related and explained by his involvement in TheRedPill meme cluster. For the time being, I make no claim one way or the other about other "high quality PUAs".

Do also note that I really am criticizing a subculture and meme cluster here. AIUI, this has nothing to do with idea spaces in a more general sense, or even factual claims about the real world. Again, connotations and attitudes are what's most relevant here. Moreover, I'm not sure what gave you the feeling that I am "cultivating hatred and negativity", of all things. While it's quite true that I am genuinely concerned about this subculture, because of... well, you said it already, the real issue here is Kay's providing enablement to it, with the attendant bad effects. (Of course, this may also apply to other self-styled PUAs).

Well, you can find a lot of magickal or Neopagan symbolism in The Matrix if you know how to look for it. The word "matrix" itself means "something motherly" in Latin, and its use in the movie could be viewed as a reference to the Great Mother Goddess. (More specifically, the Great Mother is actually one archetype of the feminine Great Goddess of Neopaganism.)