During the time the Bible was written, people's understanding of the world was primitive. The only reason that "spilling a seed" was condemned because they did not know of eggs and ovulation, believing that the man's semen was the child in of itself. Masturbation was conclusively murder. They also lived in a time where their numbers were scarce and preventing the population from growing was treason. From a pamphlet I once read about homosexuality and the Bible:
"The Biblical authors knew nothing of homosexual orientation as we understand it, and therefore said nothing to condemn or approve it."
He also says the Biblical authors believed the earth was flat and the sun moved up and down.
"There is a growing body of evidence from science, psychology, history, psychiatry, medicine, and personal experience that leads to a clear verdict: Homosexuality is neither a sickness nor a sin. Unfortunately, the church has always been slow, if not the last institution on earth, to accept new truth."
We cannot depend solely on the Bible, which we all know is thousands of years outdated, to strictly run our lives. It can be used as guidance, like "love your neighbor," "give thanks to your parents," simple stuff like that. But our understanding of the world has grown so much now; the customs developed then can't always apply to us. I have a Jewish friend who, once on Passover, ate a muffin sandwich with eggs and bacon. ("Triple whammy!" he said) He told me that pigs are not considered kosher because they were dirty and thus diseased. Meat and dairy shouldn't be eaten together because the animal cannot digest in its mother's milk. But given the way food's processed nowadays, he said, there is little chance of disease from pig meat and that the carton of milk you're drinking is most likely not related the steak you're eating. We also consider pedophilia and necrophilia taboo as well, even though it isn't mentioned in the Bible. And the difference between homosexuality and rape is that there is no love in rape and it could very well be a threat to the victim's life.