It is germane to point out that it isn't simply "political" writing or blogging. Moldbug has several essays that are explicitly racist, and though he would no doubt dispute the relationship, the vocabulary and arguments he uses are virtually the same as those of modern Nazis.
Strangeloop, in the past, has explicitly tried to foster a minority-friendly environment. Many of the other speakers are from minority groups. It's easy to see that having a speaker with Moldbug's history would do irreparable damage to what Alex has been trying to do.
You can still disagree with the decision, but that at least is the context in which it was made. It isn't just that he's politically conservative or holds to some unusual opinion - he has literally written that several of his co-speakers are genetically more fit to be slaves while he, a white male, is genetically designed to be a master.
I don't blame Alex for wanting to avoid that dynamic at his conference.
Call it "culture fit", if you must. Can't he have the culture he wants at his conference?