In reply to:
"We have to guard others' freedoms as closely as our own. Or we all end up with none."
Uhh.... actually.... no. There is nothing to guard.
He has no "freedoms" or "rights" as a DJ other than the right to not have the GOVERNMENT interfere with his speech. .
1: The relationship between the Government and it's citizens are "rights".
2: There is no similar protection for the relationship between an employer and employee. You have no freedom of speech in the workplace. You do have the freedom not to be discriminated against in hiring for (race, religion, creed, sexual oprientation) but not for much else. YES you can refuse to hire NRA members. Tough Noogies.
So: He is an employee and will do whatever he is told to do by his employers or he will no longer be an employee. That's basic.
Oh well... if you are out of sync with your clients, you'll lose business. Lesson learned.