What is the principle of contradiction? In a nutshell, it’s this: a thing cannot be and not be at the same time. Saint Thomas Aquinas shows that not even God can deny the principle of contradiction, the absolute law of the order of being, because it is impossible for God to will the absolutely impossible.
Regarding the immorality of contraception, Familiaris Consortio explains that "every action which, either in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible" is wrong.
"While Jesus was kind to sinners and to those who went astray, He did not respect their false ideas, however sincere they might have appeared. He loved them all, but He instructed them in order to convert them and save them.