If you regard the bartender as homophobic, does that mean you wouldn't pay him for beer (since, believing and saying things you consider reprehensible, you've deemed him unfit to receive money)?
You seem to be missing a rather large point - the bartender is unlikely to use his position to promote his views in the way that Card can. However, if the bartender is flying a flag in his bar that proudly proclaims "Faggots aren't human" or other reprehensible statements, than absolutely he's unfit to receive my money. Would you happily hand over your money in that case? Surely there's some viewpoint you find reprehensible - would you willingly immerse yourself in it simply because the wings are good?
The artist or celebrity that uses their position to promote any viewpoint should indeed be regarded in light of those views. That's not to say their art, or service, should be regarded as such, but it should by all mean affect what I do with my money.
And let's not forget it was Card that made a choice to use his position to promote such views and used his position as an artist to gain exposure for them. So why should the 'art' be separate?