Perhaps the longer days, warmer weather and start of the Crit and Track season will see things becoming a little more positive and constructive - similar to the help I've been getting on the road course.
I hate to be negative, but that's never going to happen.
There's a subtle difference between friendly banter amongst club mates on the road and participating in an Internet forum where everyone's opinion is correct, and indesputably so (especially if they're in the minority). After a while you learn to just sit back and enjoy the entertainment. If a topic ever starts to fizzle you can always lob a bomb of your own in to spark things up again. That's what the Internet is for after all.

I disagree Jock. Just a small amount of effort will improve things a lot. Firstly, the forum should be setup so each post is approved by the admins. The admins will be able to decide whose opinion is correct prior to the post becoming public. This will stop a lot of the negative stuff being posted for all and sundry to see.
Secondly, there should be a members only area. By this I mean actual club members and not just registered users of the forum. This area would allow posting without admin approval but could not be viewed by non-members. This area could be policed by the admins and any negative posts deleted. Repeat offenders would be banned or perhaps have championship points deducted particularly if they're also racing negatively.
Thirdly, an area for viewing only by committee members should be created. Other members with a proven history of positive posts and positive racing may also be allowed to join that area. If any of these positive members became negative, they would be banned from that area. Of course, discussions about this part of the forum would not be allowed in public. Alternatively, a secret handshake be created so that it's clear whether content of that forum could be discussed when on a coffee ride.
So you can see how easy it is to have a positive forum. Just better organisation really.