That's the thing, in a proper sense (as far as informal fallacies go), an ad hom is not the same thing as an insult. There is a term for that, it's "insult." An "argumentum ad hominem," an "argument to the person," is the false refutation of the other person's argument on the basis of that person's own attributes when those attributes are not relevant. This gets flanderized to "insulting who you are arguing with" because of dumb debatebros trying to do gotchas ("You insulted me, I win!") along with the issue I expressed before about how it can be very complex to formalize a prose argument because of the sheer volume of things that could be left to implication, e.g. if I call you an asshole and say nothing more, what does that mean as a response to your argument? That it's wrong and you're an asshole for saying it? That what you say can be dismissed because you are an asshole? etc.

The case that I am making is that the thought-terminating label is done as the scaffolding for an ad hominem. If someone wants to feed the poor and I, as a reactionary, know little else about them, then to an American audience something like "That would be communism" pragmatically functions as multiple implied arguments, first the arguments for why I would call it communism and secondly the arguments for why it is bad to feed the poor. Because of context, we can supply premises and conclusions that in this case are around 5 times longer and collectively much more complicated than the literal assertion, some cartoon version being: "Handouts are communism, feeding the poor is handouts, feeding the poor is communism; communism is bad, therefore feeding the poor is bad; we should not do bad things, we should not feed to poor. QED"

Without exaggeration, the pragmatics of such a situation suggest that that little four-word sentence functions as the presentation of that entire argument. Incidentally, the argument I just produced is a version of the phenomenon you're talking about, just directed to be about a policy proposal. A slight change in the framing could make it involve an ad hom.