Under what circumstances should a vendor be required to do business with someone?
I think we can all agree that shopkeepers should not be permitted to refuse service to someone because of race, creed, sexuality, etc. I think we can also agree that they should be permitted to refuse service to someone in a Klan hood, or a Westboro church member, or someone with a history of dine&dashing, or other disruptive behaviour.
What about someone who's widely known in the community to be disruptive, but hasn't actually dine&dashed at that particular establishment - can they pre-emptively refuse that person service? What if it's a celebrity with a well-known image that involves public nuisance - Justin Bieber comes to mind. Should a restaurant be able to turn away Bieber at the door, just because of his reputation?
Should a pharmacist who believes abortion is murder be forced to fill a prescription for an abortifacient? Should a pharmacist who believes that birth control is morally abhorrent be forced to fill a prescription for birth control pills? Should a convenience store owner who believes extramarital sex is wrong be forced to sell condoms and lube to someone without a wedding ring?
What about politics? If someone believes a certain war was declared unjustly, should they be able to refuse service to soldiers who participated in that war, or to politicians who authorized it, or a citizen who campaigned in favour of it?
What about crime? Should a vendor be forced to sell their wares to O.J. Simpson or to George Zimmerman, if they believed those men committed murder and got away with it? Should they be forced to sell spray paint to someone with a history of vandalism? Should they be forced to sell candy, dolls, zip ties and a video camera to a known sex offender?