"not in cases of emergency, but in the normal course of business"...Draft is morally permissible to defend the homeland."
Defense of the homeland is not something that can be put away in a closet until we are attacked. For instance, highways and bridges figure in to national defense.
It is foolhardy to wait for emergency before thinking of defense.
"Routine national service under any other pretext is temporary enslavement of the conscripts and is malum in se."
Nonsense. It is not only moral but Constitutional to require a certain amount of service from members of society. To propose otherwise leads inexorably to the position that every requirement laid on us is slavery, from military service in time of war to taxation and child support.
You propose "defense of the homeland" as your requirement for conscription, but that's as arbitrary as any other position. Someone could easily say, okay, our country is in a state of emergency due to the failure of parents and our social institutions to turn young people into civilized human beings. Draft'em, send them to boot camp, and civilize them. They get their discharge when they pass the GED.
There is no question here that we want the country to have the power to require some things of us under some circumstances; we're just quibbling over how much and when.
Defense of the homeland is defense of life and property of the fellow citizen against an invasion. The rest is aggrandizing the state under one pretext or another, which is immoral for a Christian to contemplate. In particular, building up a cadre of militarily trained youth in anticipation of some imaginary invasion at some unspecified point in the future whets the aggressive instincts of the state and is a grave sin.