Also, since many people use this same Rambam as a source for army exemption:
R’ Shlomo Aviner writes (translation)”Ha-Rav Tanenbaum, who was the secretary of the Va’ad Ha-Yeshivot in Israel, heard from Ha-Rav Isser Zalman Meltzer that it is a falsification to claim based on this Rambam that yeshiva students are exempt from military service.”
and R’ Aharon Lichtenstein writes “Even if we grant that the Rambam’s statement does imply a categorical dispensation in purely halachic terms, it remains of little practical significance. We have yet to examine just to whom it applies. A levi is defined genealogically. Those who are equated with him, however, literally or symbolically, are defined by spiritual qualities; and for these the Rambam sets a very high standard indeed. He present an idealized portrait of a selfless, atemporal, almost ethereal person – one whose spirit and intelligence have led him to divest himself of all worldly concerns and who has devoted himself “to stand before God, to serve Him, to worship Him, to know God; and he walks aright as the Lord has made him and he has cast off from his neck the yoke of the many considerations which men have sought.” To how large a segment of the Torah community – or, a fortiori, of any community – does this lofty typology apply? To two percent? Five Percent? Can anyone… confront a mirror and tell himself that he ought not to go to the army because he is kodesh kodashim, sanctum sanctorum, in the Rambam’s terms?”