It's simply an arbitrary, irrational, and unsubstantiated stance. Sure, the bible says that it's a "sin", but the bible also supports slavery, selling your daughters, and condemns to death those who eat shrimp or pork, rotate their crops, have tattoos, trim the hair around their temples, speak to menstruating women, or work on the sabbath. All stuff that today we acknowledge as nonsensical garbage, but yet we're still hung up on homosexuality? I hate to break it to you, but those ancient savages might've been wrong about a few things, and just because they claimed to speak on god's behalf doesn't mean that they actually did.