It's the law. You can't discriminate against a couple solely because they are gay or lesbian.
Anymore than you can discriminate against blacks or Roman Catholics or disabled people.
If skinheads want meat from a kosher butcher, and they are polite customers, they have every right to be served. If they harass the butcher, that's criminal behavior.

It is amazing how many people were fine with civil rights laws -- until they included gay people.