One of the great evils of contraception is that it establishes as a working principle that modern man and woman can take apart what God has put together. That’s what contraception is all about — taking apart what God has put together in the marriage act. Once a culture accepts that “philosophy,” it cannot say a firm “No” to any imaginable behavior between consenting persons. In that way of rationalizing, all that counts is mutual consent so adultery, fornication, sodomy, prostitution become logically permissible. The natural law is abandoned. One dissenter wrote that his rejection of Catholic teaching on birth control also involved his rejection of the natural law, and that meant he had no way to say no even to bestiality — humans having sex with animals. That is the logic of contraceptive birth control.
John F. Kippley
Natural Family Planning: The Complete Approach
Sex and the Marriage Covenant
Battle-Scarred: Justice Can Be Elusive