More wisdom from JPII on marital sex and the need for it to be open to procreation of new life with God:
 

In the world of persons…instinct alone decides nothing, and the sexual urge passes, so to speak, through the gates of the consciousness and the will, thus furnishing not merely the conditions of fertility but also the raw material of love. At a truly human, truly personal level the problems of procreation and of love cannot be resolved separately. Both procreation and love are based on the conscious choice of persons. When a man and a woman consciously and of their own free will choose to marry and have sexual relations they choose at the same time the possibility of procreation, choose to participate in creation (for that is the proper meaning of the word procreation). And it is only when they do so that they put their sexual relationship within the framework of marriage on a truly personal level.

 
Ding! Can you hear that? It’s the harmonious melody of truth.
 
We have been taught our whole lives that contraception is a Good Thing and that it’s okay with God to do. Even most Protestants believe this, and as a result the most sacred act of their marriages becomes perverted from the tremendous good that our Lord made it for. Instead of bringing the married couple closer together and closer to God with every joyous act, it actually pushes them further away from one another and God.
 
They need to know the truth! If they understood the fullness of the truth of how God made them, they would never want to use contraception and hurt their marriages and God. But most of them have never even heard this truth before, so we have the amazing and challenging duty to teach them. We have to come up with ways to share this truth in a way that won’t be immediately rejected by our separated brothers and sisters.
 
One great way to do it is to buy these CDs from the gift foundation and give them to your Protestant friends. They are inexpensive and deftly broach the subject without explicitly saying it is “Catholic” theology.