One of the most perennially popular courses at my alma mater was entitled "Murder". It was an exploration of the moral justification behind state-sponsored violence, from capital punishment to war to genocide. The realization that most violence is morally motivated comes with interesting quandaries when you consider what the response to such violence should be. Say that society successfully develops the norm that vio…
> What do you do with people who do not agree with this norm? Are you justified in using force against them? Annoyingly enough, the Quakers -- despite being doctrinaire pacifists in all other areas -- answered this question with a resounding "yes". Flogging, stocks, and various other brutalities (I don't remember if they used capital punishment, but I think they did) were routine in colonial Pennsylvania...
Capital punishment's issues primarily stem from the fact that you're using an exogenous body of collective action (the state) as a proxy to put people to death, with all the problems of public choice that come as a result.