As Catholics, we believe that it is immoral to take a natural instrument created by God and use it for unnatural purposes. If you were a watchmaker that created a watch, you would say that it is good if it tells the correct time. If it does not tell the correct time, as it was designed to do, you would say that it is bad. Just as God created everything good, they only remain good if we do not pervert their intended design and purpose. If procreation is consciously blocked, we are perverting what is natural and good. Procreation, which should be done only within the sacramental confines of matrimony, is reduced through contraception from being unitive, covenantal and life-giving, to that of a selfish and destructive act. It is a hallmark of the Culture of Death.
Gen 1:28, 9:1,7; 35:11 - The Lord God commands us to be fruitful and multiply.
Gen. 38:8-10 - Onan is slain by God for practicing contraception.
Lev 18:22-23; 20:13 - Wasting seed with non-generative sexual acts brings the judgment of death.
Deut. 23:1 - Whoever is castrated cannot enter the assembly. Contraception is contrary to moral and natural law.
1Cor. 7:5 - Married couples should not refuse each other except by agreement, naturally. Natural Family Planning .
Rom 1:26-27 - Sexual acts without the possibility of procreation is sinful.
“Because of its divine institution for the propagation of man, the seed is not to be vainly ejaculated, nor is it to be damaged, nor is it to be wasted”… “To have coitus other than to procreate children is to do injury to nature.”
St. Clement of Alexandria, The Instructor of Children (A.D. 191)
“Women who were reputed to be believers began to take drugs to render themselves sterile, and to bind themselves tightly so as to expel what was being conceived, since they would not, on account of relatives and excess wealth, want to have a child by a slave or by any insignificant person. See, then, into what great impiety that lawless one has proceeded, by teaching adultery and murder at the same time!”
St. Hippolytus of Rome, Refutation of All Heresies (A.D. ~215)