[uncertaindrumer]

Where is the basis as in, where does the Church say so? Or where is the basis, as in "Why does the Church say so"?

In terms of the "why", it is because condoms pervert the intimacy of marriage, taking the pro-creative aspect of it away, which is not what it was intended to be. That is the SUPER short form. Also, the only time a man ever contracepts in the Bible, he is killed.