The problem with the draft is that you end up with a lot of unmotivated people in the military. With an all-volunteer army, you're dealing with a lot of people who not only don't want to be there (similar to draftees in our other wars), but also actively oppose the aims of the military (unlike, say, WWII draftees, but similar to Vietnam-era draftees). Which causes problems that affect military readiness. There's a reason why the military embraced the all-volunteer concept.
But Vietnam was a special case, imo, one that has never occurred in our history before or since. I do think the way to approach it is the way it's been done by almost all armies down through history: You draft people, you put them on the front line, and you tell them, "fight or die."
One thing we have to remember even about Vietnam is that our draftees performed well, and the thing that lost the war was not our draftees, or anything else about our military, but democrat politicians and the squawking leftists they pandered to. IMHO.