Why are people so mean to gay/s?

if people think that racism is wrong then why would they think that being mean to gay people is ok? im straight but i have a few bi/lez friends and they are afraid to come out of the closet because they are afraid that people will beat them up and make fun of them. one of them hasnt even told her parents! they are really religious and they would probibly disown her or something if she told them. i feel sooooo bad for them! i mean love is love right? does anyone know why people are soo mean? or any advice for my friends?