Where did Christianity get these bizarre hang-ups regarding sex? I'd point my finger at the first Vatican council. The vow of celibacy was added in the middle ages, to increase the standing of priests among the public, amid rampant accusations of impropriety. At the time, celibacy was a higly regarded moral stance, as the culture of Europe in the middle ages widely villified sex. One of the main proponants of celibacy was St. Augustine.
No, I'm not going to pretend that I'm a biblical schollar. I have, however, read quite a bit of biographical information on Augustine. He certainly did love the pussy, before he decided that lust was carnal and evil. It's systematic of a lot of Catholic irony. I fail to see what evil comes from consenting adults finding pleasure together. The social evils of fornication are naught, compared to the physical violence of sexual repression. Anyone ever seen a serial killer? Their concept of sex is the same feeling of shame and

Thus comes the belief that sex is intended purely for procreation. The passage "go forth and multiply" is cited, making oral sex, vasectomy, and masturbation sinful too. If your hormones, which any supposed God designed you to have, act up and you masturbate, are you really sinning? Is there any real definition for "sin?" Which is more wrong, going against the doctrines of the church, or maintaining a respectful attitude for the health and dignity of your neighbors? There's a socially healthy context to masturbation. You don't avoid healthy relationships just so you can spank your monkey, but fearing these natural impulses and calling them "sin" only reflects ignorance about yourself. Nothing in the Bible prohibits masturbation. It was made sinful by the Church for political reasons, decreed by guilt-ridden theologians like Augustine. Incidentally, he castrated himself. That also goes against church teaching.
A most unsettling thought, our modern understanding of sexuality has not caused the church to rethink it's abhorence for masturbation or sex. Conservative Christians are called to feel terrible pain and guilt about sex. In Catholicism, this has led to the rise of "cafeteria Catholics:" people who pick and choose when they listen to the church. It's really the only logical solution. The Church is perfectly aware that sex is not itself inherently destructive, nor is it "evil" (reading Papal Encyclicals on sex will show you that), but they still harp upon the bedroom like it's some great dungeon of evil. Part of it is based on the writings of St. Paul, and part of it is based on teachings which surfaced in the middle ages, and part of it is based on a reactionary response to society's openness to sex.
In fact, the bible itself does not explicitly ban premarital sex between single, heterosexual couples (whereas, the Church's view of sexuality would cause one to think that this was, in fact, the case). The church's modern position on coupalation surfaced out of secular political governments regulating sex. This is supported by the fact that marriage was not defined as a sacrament until the middle ages, and in fact many supposedly holy men of that time had either multiple wives, harems, or concubines (for instance, Charlemagne.)
As a former Catholic, I've made my peace with the church. My former faith has done some positive things for me, but there remain several disgustingly repressive, creepy, and anti-intellectual strains of thought within the diocese. It's too much for me to ignore. The old spectre of European theocracy is still too strong in the Vatican, and I fear much of the clergy still get off on controling their flock through harassment and intimidation.
Like in this instance.
LinkRELIGION
Nebraska Catholics warned of alliances
Published March 11, 2005
LINCOLN, Neb. -- The Vatican has let stand a 1996 order from Lincoln Bishop Fabian Bruskewitz that his parishioners must sever ties with 12 groups or face possible excommunication, the Lincoln diocese said.
Among the groups are the lay reform organization Call to Action, abortion-rights advocates Planned Parenthood and Catholics for a Free Choice, and several Masonic organizations. Bruskewitz said the groups contradict Roman Catholic teaching.
An appeal was filed with the Vatican, but the Holy See notified the bishop that the appeal was rejected, said Rev. Mark Huber, a spokesman for the diocese.
Huber said last week that Catholics who affiliate with the groups have two months to sever ties with them. Bruskewitz has said that parishioners must search their consciences to decide whether the warning applies to them.
Excommunication is a severe penalty under which Catholics cannot receive Holy Communion, or be married or buried in the church. They can, however, restore their communion with the church through confession.