The government requires them to serve people they would rather not serve right now. I would think that the freedom to cater to whomever you want to would more than offset a requirement that you clearly identify those people ahead of time. Looking at it another way, it allows the market to decide who to patronize and who not to.
People have a right to be @$$holes, even though we wish they wouldn't. Trying to use the government to stop people from being @$$holes seems like a bad idea.
I don't see it as the government trying to stop people. I view it as a encouraging freedom of choice and promoting open markets where everyone has the same information. What you seem to want is to allow people to be @$$holes in secret and not bring it out until the consumer has already wasted their time coming to the shop in the first place.
That people aren't informed by signs doesn't make it a "secret." For most of this country's existence, the idea of refusing service to homosexuals would have been regarded as "normal." It was the default condition of every business.
I can see where a sign would simply invite harassment from homosexual groups, and the history of their movement has shown that they will get dangerously violent if necessary to push their agenda.
The only reason homosexuality has been removed from the list of psychiatric disorders was because of a campaign of threats and intimidation from homosexuals against the doctors making up the American Psychiatric Association for years leading up to their 1973 decision.
Doctors were threatened if they didn't vote to remove homosexuality from the list of disorders.
I do not believe homosexuals are entitled to know that their patronage would be rejected by the business owner, because this would make such businesses the targets of intimidation campaigns. (Ala Kim Davis in Kentucky)
Homosexuals should either be cured or go back in the closet. They absolutely should not be indulged.