"Really, what are you afraid of with readers’ comments? " asks MT from Pt Piper.
Since you insist, additional to the reason above about wet blankets, the establishment is gaining control and in more countries every day privacy and defamation laws affect website content. Sites that allow comments should be protected under original laws for anonymous or defamatory statements made by a third party in a self-serve post (comment).
On the defamation front, increasingly, laws require online publications and websites to publish a correction within ‘n’ hours of receiving notice of any content that anyone believes is detrimental to their image. A website that allows users to comment on content could face potentially enormous liability risk if the blogger or a third party user expresses an opinion that offends the most thin-skinned – or worse, mischievously malicious – ahole. And we haven’t got to worry about anonymous commenters, whose identity gummints increasingly legislate to make website owners reveal.
Finally, and this is a theory, if a comment includes a website deemed by the puritans who maintain the Australian goverbments “black list” of prohibited websites, then this site might be added to said blacklist, or cop a fine. Or both. Even if the link was in plain text in their comment, which is possible and not affected by live links being disabled in comments.
Say goodye to the little guys on the web.