basing states' moral rights on the monopoly of violence (instead of secondary concerns like avoiding the tragedy of the commons and establishing a baseline living standard) opens the door to justifying pretty much any violent state action. Governments having a monopoly on violence means they technically have a monopoly on genocide too, but that doesn't mean it's morally acceptable.

And just about any violent state action happens various places and nations get away with that all the time.

A lot of people are confusing what reality is with how we want it to be.