The idea behind integrating the National Guard and Reserve into deployment plans was to insure that operations had the backing of the general population, at least in theory.
Bluetrain, actually the Guard and Reserves were always supposed to be in the role you describe. However, during Vietnam, Lyndon Johnson refused to activate them fearing loss of political support for the war resulting in the Guard and Reserve being a place to hide from the draft and the war with the regular Army being populated with "McNamara's 100,000" which was a disaster and almost ruined the force. GEN Creighton Abrams (the one the tank is named for) said "Never Again!" and developed the Total Force concept that insured that the next time America fought for a prolonged period the Guard and Reserve would have to be used and if the populace who supplied those soldiers grew tired of the war they would force the political leaders to end it. That happened and now we have a new President who will do just that.
As to the militia, if regulated by the proper elected officials and trained appropriately you could be right. What would not work is a mob with guns who might be as likely to violate our rights as preserve them.