Ugh, this debate has been dragged so far from the original point. The purpose of this law is not to protect any students from bullying, nor is it in place to ensure that Tennessee remains a bastion of high quality education (read as much sarcasm into that phrase as you feel is appropriate). The purpose of the law is to preserve outdated conservative ideals on modern social issues, and to deprive students of vital information regarding sexuality so as to "protect" them from growing up. Some people may have been led to agree with this law on that basis, but that's not actually why it exists. If the law were actually about keeping irrelevant social debate out of the classroom, why not just ban discussion of any controversial social issue including abortion, foreign policy decisions, the bailout, the president, 9/11 or religion?
The fact of the matter is, Tennessee lawmakers don't want kids being taught that homosexuality is OK. They can't stop the parents from teaching their kids that, but by god, teachers are fair game.