It has been my experience that students believe, initially at least, that the Church condemns the use of contraception because it is unnatural, while She allows the use of Natural Family Planning because it is natural. But this is not so. The fact that one method is natural and the other is not morally relevant. There are many things that are unnatural, which are not immoral. Rather, the moral nature of an action is determined by the relationship that exists between the will and the basic intelligible human good that the will bears upon - in this case, human life.
Contraception is a life issue, primarily.
From this angle alone will we be able to see that there is a very real difference between the legitimate use of Natural Family Planning and Contraception. But before we go into this, we should recall some general principles relating to the life issues. First, we shape our moral identity by the choices that we make. It is not true that 'you are what you eat'. If that were so, most of us would avoid fruit and nuts, as Garfield once said.