Parrish, I’m curious if there’s anything in libertarian punishment theory that would justify a victim, or victim’s agent, using force to keep her assailant disarmed. Off the cuff, if the crime is “gun disarmament,” then wouldn’t both estoppel and proportionality justify forcible gun disarmament of the criminal? That seems compatible with libertarian punishment theory. Another may be the crime of “waving a gun around and threatening people.” Threats are as good as actions, so criminal disarmament of the perpetrator of such a crime would be justified as a matter of self-defense, at least until the perpetrator repents (to be determined by norms and conventions in a free society).
Of course, it does not follow from the above that “the state,” the group of people illegitimately monopolizing the provision of law and order (or the legal use of force), is justified to enforce criminal disarmament, exactly as you say.