Just so it's clear, you are simply arguing that people should be able to discriminate, so long as they make it clear that their policy is to discriminate? Is that genuinely what you're proposing here? That discrimination is okay if you just state that you want to discriminate?

And I would love for you to be more specific in your examples. What exactly are customers doing that "go against his religious beliefs"..? Beyond that, what would be the difference between, say, a religious person denying service to gay people vs a non-religious person denying service to gay people, and why would one be okay but not the other? If you deny a service for all people, then that's okay, but denying a service to certain people is not okay; as a classic example, if a baker knows that they will not make a wedding cake for a gay couple, then the only thing they can do to not discriminate would be to not make wedding cakes at all for anyone, which would be a perfectly viable option for a homophobic business owner. They could even put a sign out front, like you suggested, that says "we do not make wedding cakes" or something. But putting up a sign that just says "we do not serve gay people" is blatantly discriminatory, and is fundamentally no different than before the Civil Rights Acts when business owners were allowed to put up signs like "no blacks allowed" and whatnot...it's all still discrimination, and no beliefs or ideologies can exempt you from that, including religion. If you cannot be religious without discriminating, then you either simply shouldn't run a business, or you should be prepared to accept the plethora of lawsuits and other legal issues coming your way, including probable bankruptcy. Your right to practice a religion does not exempt you from laws protecting other people from your personal beliefs.

This entire argument simply comes down to: is discrimination okay? (the answer is no)