The WWII Army was 93% draftees, so obviously they do fine.
My personal experience with draftees is that there is little difference from volunteers.
Teenagers and 20 year olds, are not exactly so fixed in their world view and philosophy and grown up determinations, that Army and Marine drill sergeants can't convert them into fighting men and make them grow up and unlock who they really are, nor can they keep some of their teen volunteers from finding out that they don't like the military after all, and that they joined without thinking it through.
People involved in this debate miss the obvious: the world and our position in it has changed. We aren’t an isolated piece of the Earth with our own little moat anymore. We have cutthroats all around us and almost a billion lunatics about to get their own individual nukes to erase us.
Somewhere along this logical path, we have get our future security together and it’s got to be all of us involved or they will erase us. We have a surplus of young self-satisfied, overweight, and lazy louts who think that they should just leave the nasty and dangerous business of learning warfare to somebody else.
Wrong. Every single citizen should be ready and able to do what the country needs - just like our revolutionary forefathers knew that they had to leave the family farm to go fight the world’s strongest army all those years ago.
A short part of our lives learning which end of rifle to use while training with all the rest of the country’s kids would good for us.
As I said, WW II was an exception, as was the Civil War. Where US volunteers excelled was in the Mexican War, Sp. American War (despite inferior weapons), even the War of 1812 after a year's worth of training.