Can you point me to scientific evidence concerning some aspects of homosexuality?

I’d like studies or scholarly articles on both sides of two issues.

1) Is homosexuality a choice or not?

2) Is homosexuality harmful to individuals or society as a whole?

I’m having a debate with someone who claims that what I believe (it’s not a choice, it isn’t harmful) has no basis in scientific fact. I said I’m pretty sure there is more science on my side than his (it’s a choice, possibly harmful). I’m looking for scientific consensus, one way or another, for either of our viewpoints. I figure we both might learn something.