You're a straight guy. You walk onto a gay bar, even if you don't want to go there... Even if you don't know it's a gay bar. Let's say  you're Lt. Harris from police academy and you just waltzed into the blue oyster wanting a drink.

Whatever the owners of that bar happen to think about you and your sexuality are irrelevant. They are required to sell you the beer. By law. Period. Done. They don't get to decide which CITIZENS they serve beer to. However much they think the art of pouring is art, it isn't. It's a beer, unfestooned with gay umbrellaa... They have to sell that beer. End of story. 

It's basic business. The tiki torch or khaki manufacturer can no more deny the sale of their product to Nazis than thr cake maker can refuse sale of a generic wedding cake, or the bartender the beer. Allowing self-determined restrictions like that opens Pandora's box, period.