Nobody's asking John to use a condom if he has a religious objection to contraception. What John is trying to do is force his religious beliefs on other people. He's wrong. If he can't serve the general public, then he needs to not be working in a position where that's his job.

Walgreens is in the wrong also. They need to fire John instantly and let all their employees know that trying to enforce religious beliefs on people who don't share them will never be tolerated.