abra cadabra: You miss the OP’s point. Let’s say there’s a guy who wants to stop learning and go to work. Right now, if he wants to work without having been in the army he has to work under the table, he can’t get job training, etc. Why is it that when such a guy is finished learning- because he WANTS to start working- he can’t do a year of national service?
And to piggyback on the OP’s question- I know the Chazon Ish said that sherut le’umi is yehareig ve’al yaavor, but did he give a reason? It would seem that, say, going to visit soldiers in the hospital would be a chesed, which is a mitzvah just like limud Torah is a mitzvah (no idea if they’re on the same caliber in the rankings, but it’s not like you’re not doing anything worthwhile in that time). If everyone thought one particular aspect of it was a problem, then start a Nachal Charedi of sherut le’umi?