Just imagine that I accuse you of having green hair and you respond "Well, I have brown hair not green"; now I go back and delete my post. Your standalone comment looks quirky at best. Let me do similar things like this to you a few times in different places and there's a good chance you don't see it or even realize it's happening. Other folks are going to start thinking you're a distinctly odd person and give much less credibility to anything you say or maybe will even start ignoring you. As I posted somewhere else, ask the question "Should all members be able to indefinitely edit or delete messages you have responded to?" and I strongly suspect that most people would answer in the negative. Speaking from past experience, when mods got to a bunfight late for whatever reason, all hell had generally broken loose. The general policy of moving things to snippiness as early as possible avoids things escalating. BTW, threads are very rarely deleted, other than spam it's usually obvious deliberate trolling - I think I could count a couple of instances where it happened over my ~3 years as a mod.