The legitimate functions of a properly limited government do not include either stigmatizing gay behavior or applauding it.
Cathy and the politicians deny that individuals have the right to contract freely, and marriage is a contractual agreement. Cathy would deny this right to gays. The politicians would deny this right to Cathy, property owners, and consumers.
Obama, who was previously on record against gay marriage, is now suddenly for it. He obviously fears a close election.