I think the legal argument can be made that slavery was abolished and you can not force someone to work for free.
Try that one out on your draft board and see how far you get. Avoiding the draft is/was a felony.
When you are drafted you get paid. In fact, you get paid just same amount as those who volunteered. In my case, that was $97.50 and found. You also take exactly the same oath (that is, swear to do and not do certain things).