] To what extent ought a blogger be responsible for the
] comments made on his blog by other people?
When you see blogger, read ISP.
If the content is, in fact, illegal, and the blogger is aware that the content is there and that it is illegal (or should reasonably be aware), then the blogger ought to remove the content. The speaker usually cannot, and so it is up to the blogger to handle it. If the blogger has, in good faith, reason to disagree with a claim made about the legality of a post on his/her blog, then he/she ought to be able to leave it up until ordered to remove it by a court.
Mind you, this is not at all how things work. This is the word of Tom.
In America, the blogger is liable if the blogger is aware of the content regardless of whether or not the blogger knows, or agrees, that the content is illegal.
] that the statements made were, in fact, libelous to begin
] with, which i'm not qualified to determine.
I guess a more interesting question is, can you libel someone on the internet. I'd much prefer to live in a world were people simply didn't believe the things that they read then a world where it is illegal to tell malicious lies. I think that the reason people take lieing so seriously is that too many people believe what they read. The more critical people are, the less we'll worry about liars. Liars loose when people think.