There was a reason the federal draft bill allowed money payment in lieu of personal military service it allowed the supporters of the draft to characterize the legislation as akin to a tax. Why was such legal mumbo-jumbo necessary? Because (in the words of Dr. Amar, the Southmayd Professor of Law at Yale University) a federal draft is unconstitutional:
Article I clearly gives Congress authority in actual emergencies to federalize the militia instead of raising an army but only under a system of cooperative federalism designed to maintain the integrity of the [state] militia. Clause 16 painstakingly prescribed the precise role that state governments had to play in training and organizing the militia and in appointing its officers. These carefully wrought limitations in clause 16 were widely seen in 1789 as indispensable bulwarks against any congressional attempt to misuse its power over citizen militiamen. Yet these bulwarks would become trivial a constitutional Maginot Line if Congress could outflank them by relabeling militiamen as army soldiers conscriptable at will, in time of war or peace, under the plenary power of the army clause...During the War of 1812, ...[Daniel Webster] argued that any federal draft under the army clause impermissibly evaded the constitutional limitations on federal use of the militia. The plan was an illegitimate attempt to raise a standing army out of the militia by draft'...Only in the twentieth century did the Supreme Court uphold a federal draft, in the Selective Draft Law cases decided during World War I. The arguments of the Court can be charitably described as unpersuasive. Less charitably, the Court's opinion can be said to resemble its contemporaneous First Amendment jurisprudence, epitomized by such now malodorous cases as Debs and Abrams...
Hence the draft-as-a-tax window dressing...
Well, hells bells, where were you in 1967? I ended up in Nam because of the draft, and now you tell me it is unconstitutional? You should have told me this long ago, I never would have gone to Nam. Oh well, such is life. I hate Lyndon Baines Johnson. Nam was his political war, just to compete with Barry Goldwater. Johnson really sucked.