I'm here for the community, not for the perl knowledge. I come to perlmonks even during the periods when I get tired of perl and write everything in ruby for a change.
I do want participant personalities. I do want to read and post irrelevant off-topic discussion in threads. I want these both for enjoyment and for actually learning things. If you don't need any of those, go to StackExchange sites (such as StackOverflow), which actively try to discourage those with the system. (Technically, the StackExchange sites have a chat part where such off-topic discussions go, but those are separated from the posts, are not threaded and you can't search information in them easily, just as you'd expect from chat.) I prefer the PerlMonks way.
As for anonymous posts, StackExchange allows anonymous questions and answers, but not anonymous comments or egg-throwing. Besides, if you don't allow anonymous posts, people can just register throwaway accounts, as long as they don't vote with them, both on PerlMonks and on StackExchange.