[Every now-and-then, I'm provoked or otherwise prompted to explain the false economy of conscription. What prompts me to do so now is the ill health of James Earl Carter, since, after all, that alleged champion of human rights restarted registration for the military draft.]
There is a wide-spread belief that the burden of taxation is somehow reduced by conscripting service. Usually the service under consideration is military. The notion is that, with a conscripted force, one only has to pay an average soldier some amount MC, whereas with a volunteer force, one has to pay an average soldier some greater amount MV. So people think that there's a per-soldier savings of MV - MC This thinking is utterly wrong.
First of all, conscription involves its own peculiar costs of administration and of enforcement. Those are far more substantial than most people imagine, and even if we use an accountant's notion of cost, the difference between the annual cost of a volunteer army and that of a conscripted army would come to less than $30 per soldier.
But an accountant's notion of costs really misses the Big Picture here.
Imagine that the state got people into the service (army or whatever) by promising them MV, but then, once they were enlisted, declared a surprise tax (peculiar to their pay) T = MV - MC That would be a tax exactly equal to the supposed savings. Defrauding them in this manner wouldn't have reduced the tax burden; rather, it would have enabled it.
If the state had used more overt force to get those same people to enlist — threatening them with imprisonment if they did not — the tax wouldn't be reduced; it would merely be disguised. Their financial loss would be just the same, MV - MC exactly that amount of tax that people mistakenly believe would be saved by using conscription. The supposed savings was no savings at all, just a tax that people failed to recognize as a tax.
However, in the real world, the draft doesn't end up getting the same people who would have been tricked by promising pay and then taxing some of it away. It draws from a larger population, some of whom might be making less money than they would in the service, but a great share of whom are making more even than MV (the pay at which enough volunteers would be found). If someone is indifferent between her job in the private sector and the job that she has as a conscript, except for the pay, then the implicit tax that she pays is MJ - MC where MJ was her private-sector pay. For example, if MJ was $60K and MC is $15K, then she is paying an implicit tax of $45K.
Because of this sort of situation, even if we ignore the peculiar costs of administration and of enforcement that I mentioned earlier, the tax burden of conscription is greater than that of paying recruits enough for an all-volunteer service.
However, in the real world, people are not indifferent between jobs (except for pay). Some people are willing to take a pay cut to defend their country; and, obviously, those people might pay a lower implicit tax (if conscripted). But other people wouldn't choose to go into certain lines of work — such as soldiering — for all the wealth in the world. The only thing that gets them into the conscript force is the fact that the certainty of being punished by their state is an even worse fate in their eyes. So let MW be the wealth of the whole world; the tax paid by each of these conscripts is something greater than MW - MC In some cases, it can be summarized thus ∞ And that, folks, is the actual tax cost of conscription.
Registration for military service was reïntroduced by James Earl Carter in an attempt to seem efficacious after the Soviet Union invaded Afghanistan. Early in his campaign, Ronald Wilson Reagan was saying that he would end that registration; but, as it became plain that he could win the election without maintaining that promise, he walked away from it. William Jefferson Clinton, who had dodged the draft as a young man, decided that young men during his Administration should none-the-less be required to register.
 I say
might because a revulsion towards the conscription itself could subvert that willingness.