DaasYochid: I think there are 2 separate issues that the chareidim are arguing about. First, there is the issue of taking people who are in yeshiva and forcing them to stop learning to join the army. Second, there is the issue of chareidim in general joining the army, because they say the army is not appropriate for frum Jews.
It would seem the first point is included in the second, except for the point about working. If a chareidi doesn’t want to serve because he’s learning, that’s fine. Such a person wouldn’t be working anyway, and shouldn’t be complaining about not being allowed to work. His entire p’tur is based on his not working! But when a chareidi isn’t learning, there is a problem. He may want to work, but can’t.
I think the answer is that the rules which supposedly make Nachal Chareidi appropriate for frum Jews must be enforced better! We’ve all seen the stories about how they tried to force the unit to do things which weren’t right. If they made Nachal Chareidi truly proper for frum Jews, there shouldn’t be a problem. Learning boys could sit in yeshiva with their p’tur, and non-learning boys could have a frum unit to serve in.