Can someone explain to me how the Selective Service is constitutional? I know Congress "shall have Power To... provide for calling forth the Militia to execute the Laws of the Union", but that's only a call, not a legal requirement for anyone to answer the call. The argument seems untenable to me. Not to mention that it's a gross violation of individual freedom, and that if you can't get people to fight for their country then maybe there's something wrong with the country.

‘The constitution is not a suicide pact’ [https://en.wikipedia.org/wiki/The_Constitution_is_not_a_suic...].

It’s the same reason there is a different legal system in the military than for everyone else.

Sometimes, you need to round up all the men and start killing folks - or everyone else dies. Such is life. Making it easy to find them is a basic operational best practice.