"If he will not hear the Church, let him be to you as a pagan and a publican." The man in question may not appeal to his conscience. He has the obligation to line that up with the teaching of the Church. If he refuses, then we treat him like a pagan and a publican, not like a Catholic who is just exercising his rights. For the Catholic Church is not a democracy, in which the authorities must dialogue with persons. Yes, all should be done in a pastoral and kindly way. But when all is done, the bottom line is: he must accept the teaching of the Church.
Suppose a man wanted to call himself a Mason, but broke with basic Masonic teachings. He would not be a real Mason at all. Similarly, one who does not follow the above teachings of the Catholic Church, especially that in "On Revelation #10" [which says: "The task of authoritatively interpreting the word of God, whether written or handed on has been entrusted exclusively to the living Magisterium of the Church, whose authority is exercised in the name of Jesus Christ."] really should not call himself/herself Catholic, but Protestant. For Protestants follow private interpretation, each one decides for Himself. Catholics follow the Church.