If you and other gay activist have problem, take it up with Catholic church and other religious entity and make it illegal to teach their followers anti-gay message.
This kid is just telling his friend what he was taught. Seems like you people are too chicken $hit to take up the big boys and only picking on the little guys.
Whatever your bigoted attitudes on homosexuality may be, gay kids have the right to go to school in a non-hostile environment. As an analogy, saying that you believe that black people are stupid, or Asians are violent, or hispanics are lazy, or any other such thing creates a hostile environment for those students. Saying that you believe someone is "wrong" by the very nature of who they are is disruptive.
I happen to think that it's "wrong" to believe in Iron Age myths and pray to imaginary deities, but if a kid said in class that he thought "Christianity is wrong" I would say he should be disciplined.
I don't know if I agree with the severity of the punishment, that, IMO, is contextual, and as for the teacher's reported interest in the subject, I might have different opinions on that as well, but this story doesn't seem to give a clear picture of what was going on there.