Gay Adoption

I found this article interesting in light of our discussion a few months back about discrimination and the Church's ban on gay seminarians. 

Religious groups and state courts are grappling with the issue. Roman Catholic bishops in Massachusetts are seeking an exemption from state anti-bias laws to allow the church to bar gays from adopting through its social service agencies. Meanwhile, a judge in Missouri ruled last week that the state could not deny a foster care license to a lesbian.

I can't remember how exactly the conversation proceeded, but there was some discussion of whether there was some contradiction between the Church's professed opposition to discrimination against homosexuals as a class and its treatment of them as the class for the purposes of its ban on seminarians with deeply rooted gay tendencies.  I don't know the back story on the Church's position on gay adoption, but it appears that the Church's opposition to discrimination against homosexuals does not preclude discrimination against homosexuals as a class when they seek to adopt.  So, opposition to discrimination does not prevent categorical opposition to admission to the seminary or adoption.  What else does it permit?  At what point does this become generalized support for discrimination with a few exceptions?