1) Bring down the quality of the military, because -- as you say -- volunteers tend to be better quality than people who'd rather not be there.
2) Bring down the political acceptability of war. If the soldiers are not there by choice than neither the voters nor the politicians will be eager to put them in harm's way.
If you want the country weak, bring back the draft. That's what this is about.
Considering there are plenty of Vietnam era vets and retired flag officers around, McChrystal’s comments are even more disturbing.
Wars used to be a lot more "politically acceptable" when we fought them to win, rather than farting around for a decade with one hand tied behind out back.
"Wars" of that latter type are obviously "unacceptable".
And should be.