Many apologists say that NFP is acceptable because it does not interfere with the natural process, even though it is directed / aimed toward avoiding conception.
These discussions always wander because people use terms incorrectly or vaugely.
NFP is not aimed at avoiding conception. NFP is what it says it is: Natural family planning. Should a couple plan a family, or should it not? Yes, a family should use prudence and wisdom in planning and raising a family.
“The glory of God is a man fully alive”. We are not accidents. Life does not just happen to us. God has left us in our own counsel to intentionally direct our lives.
Birth control is not intrinsically evil,
contraception is. When we say an act is evil, we are evaluating it morally. Contraception means a sex
act that is disordered in some way to prevent conception.
NFP can be said to be birth control, although that really doesn’t express well what NFP is ordered to. NFP is
not contraception.
People use both birth control and contraception to mean substances.
“Did you get some contraception”? Did you take your" birth control?"
Some people take “birth control” pills to regulate their hormones.
This is not how the Church uses these terms. In fact I don’t think the Church uses the term “birth control” at all in her teaching documents.
The act of contraception is what is intrinsically evil. And the periodic abstinence practiced in NFP is not an act of contraception.
People, really. Do you believe that someone with the intent of contracepting would go through the time and trouble to practice NFP? I know of literally no one who does that, and have never heard of anyone doing it.