Earlier quoted context omitted.
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…
Is that really an issue? If the user makes more uncivil comments then you flag them again until they get the picture. There are plenty of other places on the internet that seem to welcome and encourage flame wars -- they can go there to work out their resentment and then come back when they're ready.
As you note, why would they stay where they don't feel welcome?