Thread closure is a brutal tool which does almost as much damage as the existing offence, or actually does more damage. Often new threads just pop up. Or the same offending content appears on other existing threads. So little is gained except redistributing the content, as we often saw last year.
Thread closure grossly insults all the participants of the thread, both active posters and its often larger pool of lurkers.
They are being told in the most rough handed way that their rights and interests are nothing but rubbish. Our painstaking and unending efforts to persuade, seduce, stimulate, reward more activity go sharply into reverse - and it is not only the few offenders who are being punished. The innocent majority suffer for the careless or nasty few.
Since we spend endless time trying to make our users feel that their rights and interests do actually matter, in order not to drive them away, this is flatly contradictory to our work as admins.
One option is instead of thread closure to place a mod post warning the offending participants exactly where they are offending. Usually this is a minority anyway. This gives the innocent parties a route to continue and is useful solid educational work.
This is often very effective especially where a mod has won a status of respect and is known to have a firm and decisive hand. Their restraint in giving warning rather than rushing into closure, will be appreciated, and there is always the ultimate sanction of thread closure still there for them to use.
I'm not sure why this isn't used more, and thread closure less. It does quite often seem that this would be adequate when a thread was closed. But then I don't work a big board so there are issues I probably don't know.
I'm wondering though if it might help mods to have a "third way"?
What about placing a thread in suspension?
This would allow a 'cooling off period' for a mod warning to sink in. The well behaved would not feel abused, in fact they'd be pleased to see 'justice being done' without punishing them. The thread could resume after say 12 or 24 hours.
I also think there is a case for the OP to share some responsibility for their thread.
In a recent case of a thread I started I had carefully monitored it for infringement of policy which was a definite risk it carried and I knew that. I put in 2 warning statements to keep it on track and there had been quite a good discussion.
But I had to sleep! While I did so three posts arrived heading in the wrong direction. Although they hadn't really offended, the direction was there. Another post did put the thread back on track, but the crucial element which was missing was another reminder from me, or a similar warning from a mod.
Failing both those there was thread closure. Had the mod been able to suspend not close, I could have contacted them when I awoke, found an "OP Alert" and helped to avoid the damage of a closure.
Good discussion cannot be imprisoned into safe areas only. To explore and create we must step sometimes on risky ground. We could do with the tools to help us do that and I think that the current binary of open/ close thread is too blunt a tool.