He Uses His Microphone as a Soapbox
You've gathered several hundred of your closest friends and family members to see you say "I do," and the last thing anyone wants is to listen to some man with a microphone espousing the virtues of anything other than fresh beats.
It doesn't matter what the guy thinks, and regardless if you agree with him or not, you didn't hire him to make political statements or promote any set of ideas, products or beliefs. It's a free country, and the guy's allowed his opinion, but not on the job and certainly not on your wedding day. If he mentions anything non-business related during your initial meeting, especially concerning politics or religion, tell him to drag his soapbox to another party -- your wedding is a commercial-free zone.