From someone with several years of moderate volume online community moderation, the issue with post-hoc censorship is radicalization.

If something disappears, no one has bad feelings about it.

If something two people are arguing over disappears, then two people carry simmering resentment about it (ironically, likely more than if their verbal spat had reached a cathartic conclusion), that eventually manifests in their next comments, and which ultimately leads to an erosion of common decency and civility.

It's a fine line, but it's definitely a line rather than right vs wrong.