While I certainly disagree with this, sexuality is not a protected class in the US, as far as I know. Therefore, they're doing nothing wrong, legally speaking. If you or others are concerned by this, you should contact your representatives and push for a law creating a protected class for LGBT.
This was along the lines of the next point I wanted to me.
It seems to me the real problem zsdersw and others have is that discrimination on the basis of sexual orientation is not illegal.
To think that this state tax credit is ONLY being granted for religious/private schools seems entirely unreasonable to me. Would we have this complaint if the story was about a secular private school? I think not.
It's the offense to his morality that some of these schools discriminate based upon their religious beliefs that I think is the basis of his complaint, but that is apparently not illegal in GA. Therefor the solution to his perceived problem is a federal law banning discrimination based upon sexual orientation.
The broader issue of whether (indirect) tax credits helping parents afford tuition to private educational institutions is good public policy and a subsidy to the institution itself in the classic meaning of the term is an entirely different matter.
Again, is the federal income Hope Credit (among others) also a despised and disguised subsidy to private/religious universities? I think not.
Fern