I remember the trolls on Usenet, too many groups were completely destroyed - when only one in a hundred messages are real, the group just dies and the trolls win, even without feeding them.
But perhaps worse are personal attacks and cyber bullying, which can be quite vicious and, as we have seen on the likes of Facebook, have sadly lead to suicides. There is absolutely no excuse for such attacks, nor can there ever be. An earlier poster recommends one warning and then blocking - the perpetrators don't deserve even one warning, just an automatic block.
But such an approach needs a registered membership scheme, such as CNET has AND full moderation. The Mods on CNET community do a good job of removing or (politely) correcting misleading information but I don't think have the authority to remove abusive posts, though I may be wrong. Make no mistake, such an approach is onerous and if you are, say, just blogging your travel experiences, then it might be a better option just to have no commenting ability.
On one or two (literally) occasions, I've seen a post on the Community forum that I considered inappropriate but rather than feed the poster with a response, I've sent a PM to the site owner/webmaster/moderator for follow up action.
I'll give you one example of an approach to a small business site that was under heavy troll attack. My friend was a one man leather craftsman, producing wonderfully tooled, belts, bags, cases, sporrans, etc, usually to customer order. He also published a monthly newsletter on the site. You don't need me to tell you the kind of messages he was flooded with from Googling "Leather belts"!
Obviously, he couldn't close the site to input, since it was his business, so he introduced a membership scheme, which he said, cost him about 15% of his business but he thought it worth it to cut the spam and abuse. His scheme would be considered Draconian by some, he wouldn't accept email addresses from Gmail, Yahoo, Hotmail, Facebook, etc. He had a "terms of site use", which had to be agreed to in the membership sign-up process. He checked his site daily and any inappropriate comment was immediately deleted, the membership of the poster revoked without any warning being given and the IP address blocked. He had to modify the IP blocking scheme to avoid problems with dynamic IP address assignment used by many ISPs, suffice it to say, he developed a method that worked. He also moved his site to an ISP with a very good spam filter.
Overall, he cut the abusive comments by around 80%, which he considered manageable. Would you go this far?
Clearly, not allowing user input wouldn't have worked, in the same way that CNET Community relies on member input, freely offered and in the most part, conducted in an exemplary way - I suspect we have Lee to thank for that! But while it's nice to know if your online information is appreciated, if you are essentially offering your experience, then it may not be worth maintaining a comments section.
I may not agree with your opinion but if genuinely held, I will defend to the last your right to hold it and respect the spirit in which you post it. Your mileage may vary!