I disagree because requiring everyone to serve in the military would mean the following:
1. We would need more wars and other occasions for our boys to go out and shoot other people, meaning more interventionist wars that get our boys killed "for their own good";
2. Alternatively, you would have to expand the function of the military to include distinctly non-military activities, including things currently covered by private charities, thereby drastically increasing the scope of government interference and operation;
3. You would have to downgrade requirements to serve in the military, including and especially physical ones, or else risk disenfranchising people who have things like colorblindness or flat feet;
4. You would absolutely end up politicizing the military because it is the only way to become a voter, and therefore politicians would spend even more time trying to undermine the decent fellows in said military than they do now;
And for TL;DR's sake...
5. Compulsory anything is un-American. Fuck that noise.