All those who think this professor has a legal right to discriminate based on religious beliefs probably also think he has the right to discriminate based on race. Nobody can honestly believe that this guy could legally issue letters of recommendation only to white people. He couldn't. And he won't get away with this stunt either.
The professor is not discriminating based on "religious beliefs" -- he is discriminating based on rejection of a basic foundation stone of the biological sciences.
This case reminds me of the Muslim woman in Floriduh who is suing for the "right" to have a driver's license issued with a photo taken in a burqa. The state's refusal to do so is not discrimination based on religion -- it is simply a rational insistence that a photo ID should include a photograph that acutally identifies its subject.
He's not discriminating based on anyone's religious beliefs. They can believe whatever they want.
However, in order to get a *science* degree, he's reasonably requiring them to accept the prevailing *scientific* viewpoint. This seems reasonable -- if you want a science degree, you can't be philosophically disposed to reject science.
Similarly, Catholic seminaries ought to be free to refuse to pass anyone who rejects Catholic tenets on, for example, the grounds that they are devout Hindus. That's not discriminating "against" Hindus or "against" someone's religion, that's just saying that you have certain standards for whom you're going to give a degree to, since that degree certifies the person as meeting particular standards of knowledge and practice and outlook.
Should we give geology degrees to people who believe the Earth is flat on religious grounds?
Should we give chemistry degrees to people who reject modern chemistry and subscribe to belief in alchemy?
Should we give medical degrees to people who reject modern medicine and believe that the key to health is the four humours?