Loco's got the right idea here as always.
But, you also pointed out good issues.

It comes down to a serious measure of keeping people in line.
At first, it seems scary, because shit could get real.
Spam happens.

But, with the new report systems and the like, perhaps if there was a stronger arm with a bigger hammer kept, it would be less of an issue. When someone reaches their hand into the cookie jar, smack the hell out of them. People would learn eventually.

Also, Loaf has the idea as well here. Quotes and the like are an excellent tool to keep separate conversations going. Heck, if done correctly there can be like 3 convesations in a chat thread going at the same time.