There is nothing more misleading a Catholic can do than to call Christianity “the religion of love.”

Christianity is not, unqualifiedly, the religion of love. There are thousands of loves with which Christianity can have no part: love of wealth, for instance, love of honors, love of the pleasures of this world; also love of one’s neighbor, in the provincial, colloquial, community sense (that it required Our Lord’s parable of the Good Samaritan to explode); also, love of one’s family, in the possessive, selfish sense (which drove Our Lord to declare that anyone who does not hate father and mother and his own life also, cannot be His disciple.)

Christianity is not even, in the abstract sense, the religion of the love of God. It is not the religion of the love of the God we arrive at by reason. It is the religion of the love of the God Who is revealed to us.

It is the religion of the love of God-made-man, Whom we must first accept through Faith, and then must love with our whole heart, our whole soul, our whole mind, and our whole strength: efforts of love we never could make toward God had He not become Incarnate; efforts of love we now must make toward Him, as to a baby in one of our stables, as to a teacher on one of our mountains, as to a victim on one of our crosses, as to a lifeless body in one of our graves; and, finally, as to a triumphant victor over our death, and a hostage in our tabernacles until the end of time.

Christianity is the love of the Word-made-flesh Who dwelt amongst us. It is a love of Him so intense that we are willing to share it with anyone who will take it, even with our enemies.

This love of Jesus, with our whole heart, our whole soul, our whole mind, and our whole strength, is the love we are called upon to share with others. It is when a stranger has become our friend through his love of Jesus, that he then deserves to be called the “neighbor” whom we are to “love as ourselves.”

On the last day, one vast horde of human beings, who are going to be labeled “the goats,” when separated from “the sheep,” will hear our loving Jesus shout to them: “Depart from me ye cursed into everlasting fire.” I hope that on that occasion our sentimental evangelicals, our Community-Chest Christians, our American proponents of “Preach love, brother” will not be too disappointed at the astringency of Our Lord’s words.

The bolded is mine. I never trust someone because they tell me they're Catholic.

It's not heretical, it's just distinguishing between types of charity.  True Charity has its roots in the love of God, which non-catholics cannot partake of, because they aren't part of the Church and cannot obtain sanctifying grace.  Those who do not have the capacity of sanctifying grace (i.e. pagans, heretics), are not OWED the same charity as catholics, because their lack of sanctifying grace means they cannot recognize the ultimate charity, which is God and His gift of sanctification.

This is why St Paul makes the distinction of different types of "doing good":

Therefore, whilst we have time, let us work good to all men, but especially to those who are of the household of the faith. (Galatians 6:10)

Yes, we must have charity towards all men, but this is limited to natural charity.  Only those who possess the Faith can accept, and give, true supernatural charity, which requires baptism.

It is when a stranger has become our friend through his love of Jesus, that he then deserves to be called the “neighbor” whom we are to “love as ourselves.”