No, it's not all commenters on Digg. Or on YouTube. Or, or, or.
But a whole lot of them seem to be lying in wait to sink their teeth into the nearest virtual pantleg... or exposed jugular. The culture of vehement attack and merciless ridicule is still virulent in a lot of places online. (The whole "You Suck At..." meme is only the latest example.)
I've heard the advice that the you deal with that kind of attack by growing a thick skin, having a sense of humour about it, and generally hardening your heart and pretending it doesn't hurt. It's the same advice we used to give bullying victims before we discovered it just encourages jackasses to become bigger jackasses.
Anyone building or managing an online community has a responsibility to keep the oil slick of aggression out of the conversational coastal wetlands. That doesn't mean there aren't lively or even heated disagreements, but that users aren't aiming to actually wound each other. And that responsibility isn't just to users; it's to the business or organization behind the community, because that kind of toxic behaviour rubs off on their reputation.
I won't pretend it's easy, especially with the entrenched culture of an established community. But civil behaviour ought to be the expected norm of online community, not the welcome exception.