[jeremysmyth]

...judicial precedent that you can't refuse service to customers just because you disagree with their ideology or background, otherwise it would be okay to refuse service to supporters of gay marriage for example

Way overbroad interpretation. The Civil Rights Act prohibits refusal of some kinds of service based on race, color, religion or national origin, and it's pretty much the only national law (in the US) that's relevant here (I'm not counting the 14th amendment or more specific laws e.g. for disabilities).

Notably, there's no federal law protecting supporters of gay marriage. They're state-specific laws, and not at all universal.