I think a bunch of atheists tricked themselves into believing they are secular(maybe even by equating the two). When you're officially opposing the teachings of some imposing religion(perhaps one you have left) for a humanist movement, it's easy to get seduced into the mindset that it could never then happen to you; You couldn't become fooled. You don't go to church. You are so much smarter then those bible-thumpers.

So you can have your gender priests telling you right to your face what the main tenets of your religion are, with Tracts and everything. And perhaps how to go about disowning family/relatives and socially ostracizing other nonbelievers. But you're so thoroughly inoculated against the possibility that you are indoctrinated; Because popular culture has already established that that sort of thing can only happen to people on the other side on the political spectrum.

It's no coincidence that so many in the Skeptics community got pulled into becoming TRAs without much resistance. Because they've already long written off any chance of brainwashing. In a way, I guess Gender Ideology separated the Skeptic wheat(e.g. Richard Dawkins) from the chaff(e.g. Matt Dilahunty).