Fr. Ryan Erlenbush gets it right:
If any Catholic calls NFP “contraception” or “Catholic Birth Control”, then either that Catholic does not know what the Church teaches, or that Catholic is purposely abusing language (i.e. lying).
Contraception is, in itself, a grave sin (and, thus could very well be mortal much of the time) … to say that NFP is “Catholic contraception” (or a “form of contraction”, as does RK) will very quickly lead many to think that the every use of NFP (in itself, according to the object of the act) is a sin of grave matter (and likely mortal).
If we end up making a couple think that their (legitimate or only venially sinful) use of NFP is a mortal sin (by comparing NFP to Contraception), then we would wrongly convince a couple of mortal sin.
But St. Alphonsus tells us that, if we make a person to believe (falsely) that they have have committed a mortal sin, we ourselves are guilty of a grave sin (which is to say, we could very well have committed a mortal sin).
Thus, the importance of being careful with our use of language! Many, I am convinced, many of the traditionalists that keep comparing NFP to contraception are in serious danger of committing mortal sin by misleading persons in this way.
Words have meaning, abuse of language is wrong … call it a “selfish mentality” or a “sinful mentality”, but if you call it a “contraceptive mentality” you are a liar, you expose the Church’s teaching to the critique of secularists, and you mislead the faithful.