Uh huh, because that's what they were advocating for. Sure. I'm gonna do you the favour of assuming good faith, so I'm not sure if you just didn't read the operative word "supposedly" in their comment, but if not: don't be so naïve.

There are widely documented occasions on which smaller instances have been blacklisted based on entirely spurious and false accusations of "fascism". All it takes is for one large enough instance to defederate, and others will follow based on their word alone. This results in the affected instance becoming non-viable, due to absence of any visibility amongst the wider fediverse. In one well-known case, an instance was branded as "fascist" and forced to shut down because the admin refused to take censorious actions that would have been illegal in their country.

That is the outcome you are advocating for when you suggest that such instances should be "iced out". And that outcome is the "toxic community" that we should be most wary of, because it is insidious and cloaks itself in a guise of supposed good intentions.

And before you suggest that these are isolated incidents that don't reflect the behaviours of communities at large: don't forget that it was mere days ago that feddit.uk, a rather large instance, was defederated by another large instance based on entirely baseless and spurious claims of transphobia, prompting the instance admin to issue a "guidance" post that basically just reiterated the existing rules... and suddenly this was seen as ok, and not transphobic at all. Imagine if the admin had instead not issued this statement, and pointed out that the existing rules were already sufficient? The instance's anti-transphobia stance has not changed, but I don't doubt that other instances would have portrayed such a response as doubling down on transphobia and defederated. So even large instances are not immune!

Defederation should be a last resort for rogue instances that support actual problematic behaviours like fascism. It should never be considered an action of first resort based on any accusation of supposed fascism or communism. Which was OP's point. Yet it never ceases to shock and amaze me at how openly and readily people are willing to suggest such a thing.

Literally nobody is suggesting that actual fascist instances should not be defederated. Nobody needs to debate what should be done about those, because the answer is obvious, and already widely implemented (i.e. defederate). So why even bring it up, as if it's a valid rebuttal to OP's point? It's not, and it's disappointing how so many discussions on this subject devolve to comments with an absolutist stance that has a feelgood vibe, without actually analysing it for cogency to the actual discussion at hand.