Never. Either warn Alice, ban Alice, or leave it alone. Attempting to give Alice an Internet restraining order is only going to cause her to find more roundabout ways of expressing her views (e.g. dragging the conflict into other threads.) Just keep it simple.

Even more simple: If Bob doesn't like Alice's reply, then Bob should downvote Alice's reply.

Schelling was in favor of a graduated scale of punishments in The Strategy of Conflict; either by smaller degrees of punishment, or a smaller possibility of a large punishment.

That seems to be most lacking part of his analysis of bargaining tactics, historically speaking. Many historians think that strategy made the Vietnam War worse than it had to be.

But is there any formal principle behind purposefully allowing yourself to carry out only a single type of punishment?