It has strong beliefs about the fundamental meaning of human sexuality and love within marriage. The Church's teaching about these is not based on laws it has made itself. Its teaching is based on demands that are built into human nature and human dignity. The two must go together. Many people try to make sex into something which it is not - something it can't be.
Some people look on sex merely as a thrill, as a pleasure.
But we must remember the two things said above about sex. To exclude or destroy either of them would deprive the sexual act of its full meaning. A couple might use sex to conceive children without it being a sincere act of love. That approach is against human dignity. Or a couple might make love while positively preventing the possibility of conception.