I'm sorry, but I think in our current world historical evidence is stacked against you.
Humans are a political species. The ultimate form of political power within a specified region is to have the most capability for the violence within the region.
Hence, if a nation state would secede all capability for violence it would effectively yield the ultimate political power to someone else.
Within this framework a state needs some force projection capability within it's territory or it will sooner or later lose it's political power.
Projecting force outside of the nation states borders or using the force to subjugate it's own population is a different thing all together. You can have too much violence, but you can't really get rid of it with the current psychological configuration of the human species.