“Let’s assume (and I know this is a big assumption but let’s take it as a given) that the government will accommodate all of a person’s religious needs in the army or some other non-violent national service. Also, let’s assume (and this is another big assumption) that there is nothing halachically wrong with doing community service for Medinas Yisroel, in other words it’s no different than doing community service for any secular nation and government.”
If that would be true, then there would indeed be no problem with somebody who is not learning anyways or not learning anymore to go to the army/national service/whatever. (Although we would still object to the government deciding that somebody may not learn if he wishes to.) The question is only if these assumptions, particularly the first one, are indeed correct.