It would be interesting to know how many people are playing along to keep the peace, while actually laughing at the whole thing because of course no mere argument could possibly hurt them in their invincible mind fortresses

In general, I treat attempts to focus my attention on any particular highly-unlikely-but-really-bad scenario as an invitation to inappropriately privilege the hypothesis, probably a motivated one, and I discount accordingly. So on balance, yeah, you can count me as "playing along" the way you mean it here.

I don't think my mind-fortress is invincible, and I am perfectly capable of being hurt by stuff on the Internet. I'm also perfectly capable of being hurt by a moving car, and yet I drive to work every morning.

And yes, if the dangerousness of the Dangerous Idea seems more relevant to you in this case than the politics of the community, I think you're miscalibrated. The odds of a power struggle in a community in which you have transient membership affecting your life negatively are very small, but I'd be astonished if they were anything short of astronomically higher than the odds of the Dangerous Idea itself affecting your life at all.