To re-phrase the last sentence, ordinary users might not have noticed all the insults or spamming that has been hidden, toggled or deleted (in the current case: it wasn't just the videos, also image spamming, and lots of personal insults), and not catch references to content in invisible trollish comments.

You assume the best in all people, but that's just what trolls like to exploit. Why there are people who enjoy such behaviour, I don't know, but they definitely exist. I don't know when you arrived on the web: was it the blogs? Or already web forums? Web boards? USENET?

I began on USENET, where trolls had much freeer rein than on later discussion formats. And I could tell you of utter asshole-ness that I could never imagine people capable of, not pre-internet. People who notice a new user, play all nice to him/her for a while, then either turn on him/her or use them to turn on others, and repeat this with new users several times. People who make the nastiest comments to users who tell of some personal grief, say the death of a wife or being diagnosed with terminal cancer. People who use up to 30 sock puppets, jumping in and out of several invented personalities (including pedophile and neo-Nazi), and even have these sockpuppets discuss, support or flame each other. People who invest a lot of time to first appear and be accepted as a normal member, then start to incite big fights, and it turns out they lied about their identity and have done the same routine on other forums with other assumed identities before. Your alarm bells aren't ringing because you haven't witnessed such.

While I rarely understood what motivates these people (there's not much common even in the real-life persona of the few I saw tracked down: there was trailer-park white trash kid, middle-aged hermit living on a farm in the mountains, a businessman, a housewife among them), what is clear is that it's not discussion they are interested in, but attention, say when they hijack a thread (as happened yesterday). You should (as I have to) also think of the victims of trolls, for example the one whose thread was hijacked yesterday. Allowing the abuse of and driving away of people who don't regularly go bonkers doesn't make us look good in any way.

*Traitor*, n.
A benighted individual who perceives an illusory distinction between serving his nation and abetting the criminals who govern it.