Michael Sam says he's returning to his old Missouri stomping grounds, not to get ready for the NFL ... but to fight a controversial bill that some have deemed anti-gay.

Sam was in West Hollywood when we asked him about SJR 39 or "The Religious Freedom Bill," which some think would open the floodgates for businesses to openly discriminate against gays.

Michael -- who of course, was a stud football player for Mizzou -- told our guy not only has he already spoken out against the measure ... but he plans to go back to the midwest to help squash it.

Check out the clip.