Ok, my arguments in favour:
I think that it's time to revisit the arguments for this again: the site is much bigger and full of wankers than it used to be, and there is a lot of unnecessary conflict. Given that civilian moderators have been discounted, and that the community team's workload is practically Dickensian, don't you think that anything which will reduce personal attacks and thus the need for deletions would be a good thing?
I understand that Justine is worried that threads "won't make sense", but given that a) people mostly talk shite anyway and fly off-topic; and b) the hide button would be individually activated by choice and not compulsory, I don't think this argument really holds water.
There are many posters mature enough to never need to shield themselves from the profoundly irritating, and some folk are naturally imbued with a zen-like calm in the face of fucknuggetry, but for the rest of us, please please please give us the option to simply never have to read the posts of people we know invariably get on our last nerve.
I am convinced that spats will reduce; people will participate more widely and constructively in threads, instead of having to hide them once their nemesis appears; goading will become much less sustained; and the bill to MNHQ for gin at weekends will be slashed to pre-2005 levels.
What's not to like?
Another thing about threads not making sense- quite a few prolific posters have, for one reason or another, had their entire posting history withdrawn, which really does ruin threads. Plenty in Classics are now incomprehensible, for example, to anyone.
A Hide Poster button could be reversible, and would only leave holes in threads which the Hider had chosen, and obviously everybody can see the thread as normal.
Another argument that comes up over this issue is that we might lose the opportunity to educate posters in the error of their ways.
I reject this too, as I don't believe people would just merrily click Hide every time someone disagreed with them; the point is that posters who are impervious to reason and that you know merely serve to irritate you on a consistent basis, to the point where you sometimes just have to avoid entire threads or even topics, could be hidden so that you can participate in a discussion without falling into the trap of becoming tetchy or rude. And there will always be posters who take pride in being tolerant and patient, and wouldn't hide anybody at all. If they want to engage, they are absolutely free to do so.
As far as paranoia goes, lots of posters get ignored anyway, especially newer ones, or people just repeating previously-made points. That isn't bullying; it's just the way of a fast-moving thread, and a reflection of people's ease directly addressing people they feel they already "know". Heck, sometimes people get ignored, then someone else makes the exact same point and gets lauded as a genius the bastards . Happens all the time, and it won't noticeably increase.
If other major forums manage this just fine with no hurt feelings, why can't we?
If people were stupid enough to just hit Hide willy-nilly, then they'd end up with the equivalent of a Facebook group, or the decidedly dull-sounding moldies group, if it still exists.
I agree that the beauty of MN lies in its diversity, and I think most people think like that. I rather suspect that a Hide button would very rarely be used: it certainly wouldn't be likely to just exclude people who weren't your close mates, I think we are all more sensible than that.
But in the cases where the occasional poster NEVER FAILS to rile and upset you, it would make using the site ten times more enjoyable and user-friendly.