Read the full quote, he doesn't endorse bullying of gay students, just states his position, which is correct for all students.
The following is the full statement by the teacher:
"All this talk in the news about gay marriage recently has finally driven me to write. Gay marriage is wrong because homosexuality is wrong. The Bible clearly states it is sin. Now I do not claim it to be a sin any worse than other sins. It ranks in God's eyes the same as murder, lying, stealing, or cheating. His standards are perfect and ALL have sinned and fallen short of His glory. Sin is sin and we all deserve hell. Only those who accept Christ as Lord and daily with the help of the Spirit do their best to turn from sin will enter the Kingdom of Heaven. There aren't multiple ways to get to Heaven. There is one. To many this may seem close minded and antagonistic, but it doesn't make it any less true. Folks I am willing to admit that my depravity is just as great as anyone else's, and without Christ I'd be destined for hell, if not for the undeserved grace of God. I'm not condemning gay marriage because I hate gay people. I am doing it because those who embrace it will never enter the Kingdom of Heaven. And I desire that for no one."