It does seem odd the degree to which gay people are so despised, ostensibly for religious reasons. What about all the other passages in Leviticus about not eating shellfish/pork, not using mixed fabric, and never getting divorced?
It seems odd that so many people are so focused on Leviticus 18:12 (gay=sin), when so many other things that are mentioned as sins are completely ignored.
A historical/anthropological answer might go along the lines of:
Homosexuality was rife in Greek and Roman societies as it was in many other pagan societies. The early Judeans opposed Greek and Roman oppression and occupation and responded by targeting the fabric of their society by making Laws or interpreting laws (e.g. idol worship became blasphemous, homosexuality became an abomination and women were not to be treated as slaves - tho the Bible records periods when this was not the case - and some traditions continued to view women as second class citizens).
Then came the Christian era.
This semi-monotheistic faith saw the bible as a pic-n-mix. One minute the Law dictated to Moses at Mount Sinai is what makes you a sinner and you don't need the Law anyway cos belief in Jesus is all that is required, the next your actions and behavior are all important when certain things offend Paul (e.g. women and homosexuals).
If it weren't for Pauline Christianity, Christianity today would either follow the Law more closely like Judaism (and thus still be a sect of Judaism) or it would have only two rules (love God and your neighbor) and no Law.
The reason for this schism is the dilemma that faced Paul. On the one hand, Paul sought to form a new religion (after his attempts to 'convert' Jews were unsuccessful) but also needed the "old" one for legitimacy (it was the one God of Israel that gave the Law at Mount Sinai, how could Paul - a mere mortal - cancel the Law of God given to man at Mount Sinai? Interestingly in the original Greek texts, one way Paul got around this was to express that he was the reincarnation of Jesus and therefore also the son of God).
If you want to read more on whether it was Jesus or Paul who invented Christianity, see the links below.
Finally, I'd like to say that whatever people believe about your sexuality, it is just their belief. You should stick two fingers up to them and get on with your life. There's a reason you were created the way you were - it's just a shame these religions can't appreciate that. However, that is their limit, not yours.