If Christian business owners have the right to discriminate against gays in hiring on religious grounds, then surely gay business owners should have the right to discriminate against Christian job applicants.

Surely Shell oil should be allowed to show Creationist geologists the door on the grounds of incompetence.

The whole notion of discrimination in hiring is impossible to enforce. If you have ever run a business and put an ad in the paper offering an opening, you are flooded with hundreds of applicants. There are dozens of completely acceptable choices. How do you pick? You can't help but base it on just how likable they were. I would unlikely find a touchy, dour, critical, scowling Christian likable. Unless I picked someone clearly unqualified over someone qualified, the unhappy applicant has no case.