[Rich]

Proponents of statism feel they have a right to impose their opinions on others,

Proponents of a particular system of property, feel they have a right to impose their opinions on others. What's the difference between an absolutist monarch and a libertarian landowner. The monarch of Monaco or Luxembourg govern less land than some land owners accepted as legitimate Capitalists by Libertarians.

But anyway at an international level there is no government. The First and Second World war can just be thought of as vigorous competition between private security agencies. If an absolutist monarchy, is legitimate, and according to Libertarians everyone's an absolutist monarch on their own land, why can't democratic states be legitimate.

[Nunt]

why can't democratic states be legitimate.

Because they did not justly acquire the land. They took it by force.