That’s a very interesting suggestion and I’d love to see it done, actually, regardless of what I’m about to write.
The problem is that mods aren’t bot sweepers or disinformation sniffers. They’re just regular people… and there are relatively few of them. They probably have, on average, a better radar than most users, but when it comes to malicious actors they aren’t going to be perfect. More importantly, they have a finite amount of time and effort they can put into moderation. It’s way better to organically crowd-source these kinds of things if it’s possible, and the kind of community Lemmy has makes it possible.
Banning these comments makes the community susceptible to all kinds of manipulation, especially in the run-up to a US election (let alone this one). The benefit of banning these comments is comparatively very minimal: effectively removing one type of ad hominem attack in arguments that have always featured ad hominem attacks, in one form or another.
This is actually very great