I'll take your word for it that Yarvin is way on the far side of any such line, but I'm still pretty curious about roughly where it is these days.
I'll leave it at this. If I was Strange Loop's organizer, what I might have written is:
I don't know exactly how to articulate where our line is on providing a stage and a microphone to people with ideas I find repellent. I've never been in a position to need to draw that line. I'm not interested in spending a lot of time surveying it further. For now, it suffices to say that wherever the line is, advocacy for apartheid and genetic predisposition to slavery crosses it.
Incidentally, the use upthread of the term "Stalinist" is telling. Yes: if Yarvin had been a Stalinist, I do think we'd be having the same discussion, Yarvin's views seeming approximately as far to the right as "Stalinism" would put him to the left.
Second, security conferences --- at least the kind I'm familiar with --- are different from Strange Loop. Strange Loop speakers are selected on the basis of presenting interesting and entertaining ideas to the audience. There are a couple people who get Black Hat talks on those terms, but most Black Hat talks are accepted based on how important their technical contribution is. If you have a new EMET bypass technique, nobody really cares whether you're a closet monarchist, because they're there to see the EMET bypass, not you.