Not just men only, but ANYONE in the country of age for selective service.
Every illegal standing on our soil of draft age is committing yet a further crime by not registering.
If they are amnestied, this would be yet one more crime they would have to be forgiven...which doesn’t happen for citizens.
So yeah...let’s include the girls. Of whatever stripe. Let Juana of Guadalajara know that she may end up cleaning latrines for Los Gringos in Afghanistan if she barges the border.
Illegals already have to register. There is almost no exemption if you are a male, and 18 to 25.
I think getting out of non-voluntary service would be very easy, and disruptive to training and morale.