My two cents worth:
They have no concept of a “good Catholic”. Instead focus on their misconceptions of the Church, Scriptures, Tradition and the faithful.
"The Bible is, and remains the [Catholic] Church’s book, and the Bible can exist as Scripture only in the [Catholic] Church. [Joseph T. Lienhard SJ, The Bible, the Church, and Authority, p 84]
The Protestant or reformer may say every individual is the arbiter of Scripture. The diversity of ‘equally valid’ doctrine among the schismatic churches belies this.
“The notion that all religions are ultimately equivalent appears as a commandment of tolerance and respect for others; if that is so, then one must respect the decision of another person who decides to change religions, but it is not permissible to call this conversion: that would assign a higher status to the Christian faith and thus contradict the idea of equality. But the Christian certainly does believe that in Christ the living God calls us in a unique way, which demands obedience and conversion. This presupposes that the question of truth plays a part in the relations between religions and that truth is a gift for everyone and alienates no one.”[Pope Benedict XVI, Truth and Tolerance]
Protestants and reformers tend to believe they have absolute sovereignty and independence from God’s will; after all they say, ‘one religion is as good as another’, i.e. relativism. Looking inward for authority, each rationalist holds the necessary individual authority to establish basic cosmic truths. This forms complete independence from any social morality not otherwise originating from one’s interior. This degradation continues with the implied right to judge moral and civil law. The argument extended is to say that God’s laws are relative; “what’s true for you, may not be true for me”. Polls and consensus become the judge of right and wrong; rather than God’s immutable truth, e.g. abortion. And finally, in the extreme the relativism requires absolute freedom of thought in matters of morality and religion.
Morality requires a standard or a guide for our actions that is subordinated to an ultimate purpose. In the case of the most basic fundamental rules, all actions are subject to an omnipotent ruler (God). Reasoning in the light of His ultimate purpose is moral order, to govern in the light of His fundamental moral rules produces law and order-or social stability.
You will ultimately need to explain what the True Church of Jesus Christ is NOT:
*]Church is not an organ whose unique differences from other ‘Christian’ religions are deemed inconsequential. “Based on incorrect theological perspectives and is characterized by a religious relativism which leads to the belief that ‘one religion is as good as another.’“ Pope John Paul II, Redemptoris mission, December 7, 1990.
*]Christ’s Church is not reformable
*]Church is not a company of like minded believers joined together by some vague vibe of Christ’s Divinity and Christ’s humanity.
*]Church is not a democracy whose doctrines are subject to the will of men. Instead it is a rule of faith, subject to the will of God.
*]Church is not constituted and commissioned by man, e.g. Luther, Calvin etc.
*]The Church is not Scripture, THE BOOK, i.e. Scripture Alone.
*]The Church is not body of ‘believers’ saying “Jesus Christ”, rather a body of faithful “doing” Christ’s sayings.
*]The Church is not solely the body of physical beings in a brick building. Rather Church is the body of faithful souls in communion with the Church including those in purgatory, and those in heaven.
Then you are obliged to explain what the True Church of Jesus Christ IS:
There is only one True Word of Christ that resides in only one teaching authority, the Catholic Church. In commissioning the Apostles to teach, Christ created a Divine college, sufficiently of God to teach a divine Word. Any other is false. Thus we see that only a Divine College can infallibly teach discipline in an irreformable Truth. Only the Divine can receive and bind others to immutable Truth with an authority that obliges. This Divinity resides only in the Catholic Church under one head, the Roman Catholic Pontiff.
The Catholic Church is constituted for the salvation of the faithful; explicit in the doors being opened in our baptism is that she is necessary for redemption, the faithful souls given an indelible mark, the new circumcision. She is a corporate family of adopted ‘sons of God’ redeemed through God’s merciful graces given freely. “He that believeth and is baptized shall be saved: he that believeth not shall be condemned” (Mark 16:16). The Church is the Divine Motherhood of our salvation; consequently we find our devotion to the Blessed Virgin a gift from heaven. Nevertheless, the Church is simplistically defined as the “Body of Christ”. The totality of sacramental life is the Sacrament of Christ. As the Church affirms our faith, our faith affirms the Church; it is only within her that life exists. The Catholic Church becomes life in Christ. The sacraments are an outward signs of inward grace of sanctification. The Church herself has a visible and outward expression in her corporate priesthood signifying the graces bestowed through her.
“If Christ is the sacrament of God, the Church is for us the sacrament of Christ” Henri de Lubac, Catholicism: Christ and the common destiny of man, English edition 1988 , French original, 1947, p 76
One thing you must not do is apologize for our Catholic doctrine, speak boldly of those things that separate the Protestant and reformer from their Salvation.