Moderating, by it's very nature, is going to be subjective.
"Agreed, but something like, Thread locked, rule #3."
Whether rule #3 truly applies may be debatable(the subjective part), but everyone knows why the thread was locked (the objective part).
Here's where it works in HNI's favor. Someone starts a new thread about the locked one, it gets deleted or locked with, "PM mod directly for this discussion." or something like that. If the PM leads to a resolution, the the thread could be unlocked, if the truth warrants it.