It’s not posed because anarchists are masters of rhetoric or argument, it’s actually a veiled ad hominem attack to the receiver of a question.
“Oh my gosh, I can’t believe you’d even think about doing that, are you sure you’re an anarchist?”
It’s clear that the questioner doesn’t expect to unearth a secret Trotskyist or capitalist who infiltrated an anarchist group in hopes of subverting their cause. They just want to illustrate they are more-anarchist-than-thou.
This is also a tool used when you’re the person who’s being the only person blocking consensus. When the other 15 anarchists in the room disagree with you, it can only mean one thing: you’re the only other anarchist in the room.
When an anarchist starts accusing other anarchists of being middle class as well, you can count on them leaving their group soon.
It’s an anarchist death dance to accuse everyone of being un-anarchistic, tell everyone else they’re middle class and they’re not, then leave.
A similar phenomenon is also prevalent among anarchists, and that’s the trick of accusing someone who describes themselves as an anarchist as not being one at all.
“Oh, John from the IWA? He’s not an anarchist.”
“Noam Chomsky? Yeah, he’s really not an anarchist, you should stop calling him that.”
“Yeah that asshole that writes Things Anarchists Like? He’s so not an anarchist.”
It’s an easy way of dismissing an opponent or controversial figure. They are fanatical enough to believe that someone not being an anarchist somehow discredits every single word that’s come out of their mouth. They don’t have to open up a heated debate, and they also make themselves feel more secure in their anarchism because so-and-so isn’t an anarchist and they are.