Actually, that is not the case; you can't force a restaurant to serve anyone regardless of race; all you can do is force them to come up with a different (but lawful) pretext to refuse service.
I agree that it is a bit of a waste of time to make bigots reject customers piecemeal; but that is the way the law works, and I can't see an obvious solution other than to repeal anti-discrimination law in its entirety.
And that piecemeal rejection bit I think causes more harm than permitting discrimination in moderation.
When the ad says "no black men" the black man is out a few seconds reading it. Reject piecemeal and you get the very thing mentioned in the post from the prostitute above--wasting time & gas driving there.
But that's the same for every single other business that's going to find a stealth way to exclude based on discriminatory lines. If there's a restaurant that just "happens" to continuously find reasons to not let black customers dine there, any black person will waste their time going there. That doesn't mean that "White Power Diner. No Black Men Allowed" is a legitimate sign for them to put on their window.
I'm interested in minimizing the harm done--and I think that's accomplished by permitting that White Power Diner sign so long as there aren't too many diners that do it. When the discrimination is open but not widespread the cost to the victims is very minimal.