I don't think there's much ambiguity around a military's utility in forcefully enclosing the commons, or claiming extranational resources at gunpoint. I suspect people who are leery of a 'Space Force' have other reasons to feel that way. And I'd hope there are other ways of managing the sharing of things like Lagrange points than outright violence (though I suppose some body must have the capability to employ force or else any agreements made would be easily violated, yadda yadda).