One also has to look at the religious connotations of homosexuality. From what I know, the bible forbids the ACT of homosexuality.
Rather than just referring to "the bible" as if any of the words contained are indistinguishable from one another as to source, I think people should take a little more time to study context. As far as the N.T. is concerned, Jesus never said anything about Homosexuality, for instance, only Paul did, and so instead of "the bible" saying this or that when it comes to the N.T., one can only say that Paul said this or that or that Jesus said this or that.
When Christians say it was Jesus who provided the New covenant, it would follow logically that HIS words are the ones to follow. Many Christians do not follow Jesus words, however (on the nature of Prayer among other things), as they are not making any distinctions between Jesus and the religion Paul did so much to create, and so when they say "the bible", they aren't really referring to Jesus, but Paul instead. They are following Paul, which makes a certain sense because Paul was the one so instrumental in creating the dogma of Christianity.
The arguments regarding Homosexuality among many Christians invariable involve an admixture of O.T. and N.T. strains, the Paulean strain grafted on to the older source, but no attention is paid to the genesis of the attitudes in such a way that they discern between social mores that arose in ancient times, and the moral lessons Jesus taught. There is no inquiry into WHY homosexuality may have been a taboo (the need to procreate being chief among these), nor into the specifics as to the situations in which the subject arose (the misinterpretation of the story of S & G, for instance), as the taboo is simply accepted as gospel and then the arguments against are created from the predetermined position that it is wrong. It is wrong because it is written that it is wrong, and because it is written as wrong, it is wrong.
People can take several approaches to the notion of morality, one of them being that morality is a recipe. "The bible" is a cook book with precise measurements to follow that do not need to be understood in order to bake the cake. A different approach to morality would be more tantamount to learning how to cook, especially by forming an understanding of the processes involved, to the point it is so internalized that it is almost instinctive. People know right from wrong, not simply because they are following a rewards/punishment set of rules, but because they understand WHY something is moral or immoral, understand the social constructs involved, and are able to reject that which is arbitrary.
The real question isn't really whether or not it is "in the bible", but whether people approach the subject dogmatically or with discernment. If homosexuality was as important as so many Christians make it, Jesus would have been all over it. He would have railed against it just as surely as he did the Pharisees of his day, but the fact He didn't seems completely unimportant to many Christians who HAVE elevated its importance well beyond that which is mentioned in the bible.
I dunno. There is a lot of great stuff in the sermon on the Mount, and if Christians wish to rail about something, I wish more would rail against hypocrisy and greed and doing things for show, or any of a number of things that Jesus actually DID talk about, instead of making what he didn't talk about so central to their agenda.