Why are you getting aggressive? You have your opinion, I have my opinion, no need to snap.
> People are different, bodies are different
Ok, I agree. But why do you then generalize yourself few sentences before and tell us that '20-30 miles a week is nothing' and treating everybody the same? I think, I was more differentiating, I said 20-30 miles/week for a long period is already too much for the majority—not for all.
> I wore down cartilage in my knee while running through pain I had been having for a while
Ok, doesn't really make your stance better. Who says that every other runner is so wise and stops running while having a pain? Maybe most of them do the same mistake like you did? Maybe they just want to win, just want to outperform other runners, just fear loosing or just want to prove themselves that they can run more than last week—all while slowly crushing their knees. And maybe it's the dynamics or game mechanics of running itself—it's not that easy to stop.
Sorry, but the cause-effect-relationship is getting even clearer with your last comment. Extensive running can get quickly dangerous and the problem is that the runner might realize this too late.