"of course, there is nothing whatsoever that suggests that the militia need care about a government or its orders."
Absolutely! Very good point. (As I said in my reply to Dante, the militia is merely the armed public - and it's really about the sovereignty of the people - which might be exercised in somewhat different ways in different jurisdictions to reflect local capacities and needs.)
"Consider the other standing army; the police. For the first century or so, any citizen could call upon any other citizen in the execution of warrant, and there were no police or state actors"
Speaking of which, I seem to recall that - perhaps it was under English common law - that a posse in hot pursuit of suspects could require anyone they encountered along the way to join them, or else be considered suspects themselves.
Again an excellent point: the police are essentially the standing army that the founders warned us against. (Sheriffs and Marshals are a little different, with different historic origins.)