You folks all seem focused on the concept, maybe with the idea of a single post that has to be judged in your head, and how it must be easy to work it out for that one post. But I'm talking about implementation and scale.
In times of disturbance, I don't think about a single post. I think about how dozens of them can build up while none of us are looking at the site. I have in mind the cases where I've come home from work to find several threads that are 20+ pages of argument, with dozens of reports, people on both sides of it asserting the other guys started it. While you all, I am sure, feel the instigation is always 100% clear, I assure you that it is not.
I mean, unless you want us to just go ahead and be draconian a-holes with no concern for fairness. If you don't want us to do that, then we have to gather context and think about it all. What you are asking is apt to be hours of work when we actually have to do it.
And that's not even considering the unintended consequences of such policy. Morrus already alluded to them, but none of you seem to care.