OK, thanks.

I suspect that if the goal is to make bad threads peter out faster, preventing all users from contributing to a bad thread will likely achieve that goal more readily than preventing one user from doing so.

We could even do that automatically if we wanted. For my own part I trust humans more than simple automatic pattern-matchers for this sort of thing, but if y'all prefer automatic pattern-matchers to diffuse the resulting complaints that's an option as well.

Of course, if we're OK with automatically blocking the downvoted user on the thread but not OK with automatically blocking other users on the thread, then an automatic branch-freeze won't work. This might be true if there are other as-yet-unstated goals being addressed, beyond the desire to end the thread itself.

Personally, I don't like the idea of letting everyone post on a thread except the person they are responding to; one-sided conversations make my teeth itch.