What's next? Are you going to investigate your clients, their families, their gender, their money sources? Are you going to open a money laundering investigation on each bank deposit you get?

Unless it is illegal, you should not care. I think it is very unprofessional to deny service to someone because he has extreme opinions. You become just as worse as him; if not more.

It is not your right to dictate what society should do. If the government allowed them to organize the event, let them roll. Remember, if you are pro-choice, you should help get the opinion of everyone be heard.