To state it more correctly, many homosexuals have had their lives messed up, mainly by homophobes and people who claim to be Christian and who condemn both homosexuality and the individuals who are. Not all homosexuals "have had messed up lives," where they need counseling or other help to deal with issues that stem from how others treated them when they were younger. So we can blame the people like you to a very large degree for messing up their lives if they have had messed up lives.
And certainly, there is a genetic component--Your claim that "no one is born that way" has been more than adequately disproven. And no, homosexuality is not "caused by a messed up upbringing." Messed up upbringings can and do happen to people, regardless of their sexual orientation--but in many ways its been worse for homosexuals than for others. but I know plenty of heterosexuals who have been messed up by alcoholism and lots of other issues.
And no, not all homosexuals reject God; one of my best childhood friends is gay, and an ordained minister. I know he doesn't reject God; nor does he think God is condemning him for being what he is. There are, after all, a lot of different interpretations of the Bible out there, and not every Christian subscribes to your particular view.