There may be many unforeseen consequences with such a change:
Do you allow normal comments in response to fluff comments? 1) Yes - you'll need to reenable fluff to follow what the "serious" replies are referring to. 2) No - the responding comments would by necessity also be labelled fluff, even if intended seriously (just to enable being able to follow up on some throw-away remark), which would lead to a continuing incentive for fluff comments - actual fluff and otherwise - to supplant actual comments. 3) No replies allowed to fluff comments - weird circumvention effects e.g. by replying to the grandparent while referring to the fluff comment
Don't you want to read all the content some specific authors provide on LW, regardless of whether they consider it serious or just "candy-floss"? Do you then have an option for "hide fluff - except for fluff from users 1..n"? Yes - keeping such a list up to date could quickly become tedious. No - have to reenable all fluff unless you want to miss e.g. Nesov's fluff-labelled comments, which will probably still be more valuable than most people's serious comments.
The list goes on. (Eventually some may even wish for a way of rating fluff comments, leading to a secondary karma system, which may lead to a regress until someone pulls the plug and goes back to the current system.)
I ventured a short way down that rabbit hole 3 years ago. If my wretched health were to improve, that the project I would most like to work on.
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.