Not that I am, but I doubt AT&T would allow conservative Christian or Catholics or pro-gun groups to run whatever activates on their property. And you know that. Therefore a public company is discriminating as to what organizations can and can not use its property. Just because you favor one particular group doesn't make it right. But you knew that.
This is true, but maybe not out of inherent discrimination or prejudice against those groups' ideology. The reason is because AT&T wants to appear inclusive, progressive, and accomodating. In today's society, that means embracing a gay union.
Conservative Christians and gun rights groups are perceived as the antithesis of inclusive, progressive, and accomodating.