The poster is in control of a trade. The poster can choose to avoid negative karma, but only by taking the risk of the comment being hidden from many readers. (Perhaps hide fluff = fewer comments and show fluff = more comments).
It is only a little like an "evil bit". It allows the poster to escape the consequences of evil (ie no down votes) by setting the evil bit. But that makes their attempts at evil easy to filter out.
What I was getting at, though, is that labelling it a fluff tag doesn't make it one. People could use it for anything they like, and I predict it would end up being the resort of people resentful at getting heavily downvoted for their hobbyhorses.
I have never been on a Lesswrong meetup because they tend to take place too far away from my range in terms of distance and budget. Because of that, I don't know if those perform this function to everyone's satisfaction in such a way that what I'm suggesting here doesn't seem worth the effort. I hear that they're a lot of fun, and involve quite a bit of silliness, though; I find those cruelly lacking on Lesswrong proper, whether it be in main posts or discussion posts, and their relevant threads.
That's why I think it would be nice to have a forum, a place to have normal discussions, where you don't have to watch that you don't say anything stupid or out-of-line lest you unexpectedly lose karma. A place to exchange jokes, frivolities, and entertainment. A place to talk about stuff that isn't rationality or singularity-related. A place to relax and enjoy the company of like-minded folks. A place to take a more personal approach to communication, with sequential rather than branching conversations. A place to make and be friends.
Don't you think having that would be nice?
EDIT: Also, if this place does already exist and I'm not aware of it, I humbly request that you provide me a link, for which I would be most grateful.