@berlioz
Ok I skimmed through most of this thread, and this is bothering me.
Good question! The Christian* belief is that sex is for procreation at least as much as anything else including pleasure and emotional bonding.
Ok, right here I'm pretty much on board. Sex is for making babies, pleasure, and special bonding between a married couple (See Ephesians 5:31, when the married couple become "one flesh" after consummating the marriage, then the couple loves each other as they love themselves, because they become two halves of one whole.)
To divorce sex from it's natural function is seen as trying to split something's nature.
Is it though? If a married couple wants to have sex just for pleasure and bonding, why get the baby making part involved? They're not doing anything unnatural. Simply stepping around something they want to avoid. It would be careless, and in my opinion out of God's will, to have sex without protection when you aren't ready for kids.
There is also the command to have children if you aren't doing something else like living a life under a vow such as being a monk.
Where in the God's word does it say that? The Bible praises children as gifts from God, mentions how children can strengthen a family, and gives advice on how to raise children, but never does it command people to have their own. Specific people have been called to provide offspring, like Sarah and Abraham, Adam and Eve, and some others. But never does He command all of His people to have kids. Not everyone was made to be a parent.
See 1 Corinthians 7. It's guidance about marriage and not being married. Some people should marry, others shouldn't. This can be applied to children too. Though marriage and children are both gifts of God, they aren't intended for everyone. Just like other gifts of God. Some gifts can be set aside for the sake of God's will and your relationship with him.
There are natural ways to actually have sex and not children, but I believe even then it is frowned upon to use such methods to prevent having any children.
I don't see why God would want this. Sex is celebrated in the Bible, if it's under the right circumstances. It's not just for having children, and we shouldn't veiw it as such. In fact, the Bible focuses more on the emotional benefit from sex far more than it does the reproductive aspect.
As a Christian, it's of my opinion that most birth control options are perfectly acceptable for a married couple to use so they can enjoy each other as God intended. I'm not saying that not using birth control is bad in a marriage. If you for some reason feel you and your spouse shouldn't be using protection, then don't I guess. But that conviction isn't (always) from God. Maybe God wants you to have kids ASAP, maybe God wants you to wait, or maybe God doesn't want you to have kids at all. Birth control and using natural planning, as long as it's not harming anybody involved, is not frowned upon at all.
*Because of all the points I made, I don't consider this a Christian or Biblical belief. It sounds like a tradition of man started by the Catholic church, or a personal conviction.