From what I can kinda remember from history classes, the ban on contraception came about from the Early Church Fathers. During this time, those in charge had a clear vision of the goals of the Church.
Contraception was "banned" because they wanted lots of little Catholics running around: there was threat from other religions.
The thing that has always stuck in my mind is that these decisions were made by old men who - in some cases - had done ALOT of shagging around!!! This "rule" was created on the basis of someone's OPINION. Don't forget, this was during a time when people would "leave their babies to the elements" if they couldn't feed them, or if they didn't look "normal".
I think the no contraception thing has gotten blown out of proportion.
If you follow it to the letter, then you should NEVER have sex for enjoyment, and never when you cannot conceive.