Ignorance of scripture? Is this a loaded question or am I supposed to guess till we get something you like? Oh wait, there's the popular debate answer - someone that keeps to the Catechism. But they also have to abide by official decree, which means that by Papal decree a practicing Catholic should believe it is not "against the Holy spirit to burn heretics." Oh, wait - Papal decree is only understandable in light of the fact that God's truth changes from day to day. or wait no, God's truth is steadfast. No wait, we're getting confused aren't we - it's that religion thing. You have to abide by official decree but when official decree is satanic in origin, that puts ya'll in a tricky spot. So I guess the requirement for what one must believe to be Catholic is subjective to the person defining it on behalf of the Catholic church - and also is dependant on the level of historical knowledge of the person the story version is being sold to. It does change things.
I asked because you were making some kind of statement about Catholics, so I was wondering how you define what makes a person a Catholic.
In other words, if we're going to debate about what "Catholics" believe, then we have to agree on who is and isn't a Catholic before our debate can proceed.
This link on heresy might help you with understanding who the Church considers to be a Catholic. Here's a sample:
St. Thomas (II-II:11:1) defines heresy: "a species of infidelity in men who, having professed the faith of Christ, corrupt its dogmas". "The right Christian faith consists in giving one's voluntary assent to Christ in all that truly belongs to His teaching. There are,therefore,two ways of deviating from Christianity: the one by refusing to believe in Christ Himself, which is the way of infidelity, common to Pagans and Jews; the other by restricting belief to certain points of Christ's doctrine selected and fashioned at pleasure, which is the way of heretics. The subject-matter of both faith and heresy is, therefore, the deposit of the faith, that is, the sum total of truths revealed in Scripture and Tradition as proposed to our belief by the Church. The believer accepts the whole deposit as proposed by the Church; the heretic accepts only such parts of it as commend themselves to his own approval."