Mdd, it is about bittul Torah, and not just about not being able to learn forever. Even in chu”l, those who can, learn full time from mesivta (ad v’lo ad bichlal in most cases) until several years after marriage. Those very years, the ones in which someone is able to focus on their learning with some menuchas hanefesh and no or little burden of parnassah, are the ones which would be spent in the army.
Army service would be a hindrance to the typical American yeshiva bachur as much as it would to one from E.Y.
Aside from the spiritual danger (which is especially acute in those days of youth), they want to take away those ikar years of learning.
Yes, as a result of the way the system is set up, they tend to learn longer than in chu”l. Rav Mordechai Zuckerman, zt”l, used to refer to these long term learners as “Ben Gurion’s talmidei chachomim”. And yes, therefore there’s an unhealthy negative attitude, for some, to working. But that’s primarily a product of potential army duty which forces the average amount of years in kollel to increase.
If instead of drafting them into the army, they would allow them to work, many more would, but you wouldn’t hear this outcry.