I appreciate the suggestions, Scagga. I do think that pre-emptively excluding anyone from talking about a specific topic is a bit problematic.
We do try to use 'snip' editing where it's, well, basically feasible. When a thread reaches a stage where 90% of the posts in it have been reported by someone for something, a portions of those posts are inappropriate in their entirety, and most of the others refer to those posts ... 'snip' editing does become a herculean task and when the end result is likely to look like a smattering of posts that no longer make sense without context and a smattering of others reduced to a patchwork of sentences, locking the thread and moving the whole thing becomes really the only practical option.
I'm also, personally, beginning to agree a little with a view expressed in the early discussion of these forums about 'snip' moderation: knowing that a mod will edit your post to remove the insults, flames and trolling but leave the rest intact removes incentive to self moderate and exercise a little common sense. It actually takes a lot less time to read through a post you've composed and delete things than it does for a mod to carefully, in the interests of transparency, move each offensive sentence to the catacombs. So every over-the-line post is, in a way, a statement to the moderators that 'hey, your time is worth about 1/5 of mine!'.
Time out locks have been used in the past, and are of varying popularity: I got five PMs in a minute after locking a thread for a 'time out', and the opinion was firmly expressed that posters felt they had been sent to the 'naughty chair'. I note too that a mod posted in the thread earlish on, with mod hat on, pointing out the potential for the whole thing to go pearshaped downhill without a canoe or whatever, and some posters expressed a sense of grievance at the intervention.
I'd also like to point out, as a general observation, that moderators have a lot more difficulty 'cleaning' and 'pruning' a thread when people respond to flames or to flamebait. Just report the post, and if a mod isn't there to deal with it right that second, take a deep breath and give yourself a cooldown period.