Wow! The responses to this question were so hateful, I just had to add a bit of clarity. The church teaches that sex is a wonderful, holy thing in marriage, but that sex outside of marriage and with contraception destroys goes against God's design for sex and is ultimately hurtful for us.
While the church does rightfully forbid the use of contraception, it is not because sex is bad or because she wants her members to have lots and lots of children. Catholics are encouraged to use Natural Family planning (which has a 99% effectiveness rate when used correctly) to to space or avoid having children should a serious reason arise, to be personally and prayfully decided on by the couple.
if you would like more information about the Catholic church's position on any topic, please feel free to send me a question. I also have several hubs on Natural family planning and the problems with contraception if you would like more information :-)