Accepting commissions still implies artist interest in the subject. And “artist interest” is not discriminatory. It is simply artistic license. I’m not interested in horse scenes, seascapes, social issues, or mountains. I’m more into cike cans and barber chairs right now.
And accepting the commission means that you are willing to do what your client hires you to do. I can't accept a job and then say I'm not willing to work on Wednesday if the job requires I do so. If a company is hired to video a gay wedding then they can't suddenly refuse when they show up for the job. They should be allowed to turn down the business to begin with by clearly stating who they will not provide services to. Which is what this video company wants to do.