Csar: RaMBaM does not say that. He gives such a person as an example. There is a difference.
Ibmzr: To add to what yitayningwut said, check RaMBaM Hilchos Talmud Torah 3:11-12. 11 speaks about tremendous maalos of being self-supporting, and 12 gives mussar to remind you to still put full effort into your Torah. As with everything else a Jew does, the ikkar is to do it all l’shem shamayim and if you do something l’shem shamayim it should be done well and make you proud to offer it to the ribbono shel olam.