MW, that is only guys who are really learning and a situation where they are not needed. However, if guys are just lolling about they should serve. If they have time toriot they are not learning at the proper level (Rav Tzvi Yehuda would not allow talmidim to lend their names to political discussions). Rav Nachman Kahana suggested a solution. Have exams at different stages. Those who pass get a deferment. Those who don’t don’t (and BTW, when they instituted exams in Lakewood many guys lost their stipends). Guys at the higher levels will give shiurim to soldiers. IMHO, they should show their lishma and concern for Klal Yisrael by dedicating their learning to the success of the IDF and saying the mishe berach for the soldiers and the state (I don’t see how anyone can object to asking Hashem to give our political leaders wisdom).
Yekke, I am proud of those girls. http://www.hebrewbooks.org/rambam.aspx?sefer=14&hilchos=83&perek=7&halocha=4&hilite=