You are not your job, you're not how much money you have in the bank. You are not the car you drive. You're not the contents of your wallet. You are not your @#$%ing khakis.
—Chuck Palahniuk, Fight Club
One of the major problems that comes up when people hear the old adage of loving the sinner and hating the sin is that nowadays, people assume that what they do is what they are. Therefore, when the Church condemns an action, people assume this means the Church hates them personally. This is why people assume Christianity is “homophobic” or “anti-woman” when they condemn behavior like homosexual acts, contraception, abortion and divorce/remarriage. Then we get to hear a lot of people quoting Matthew 7:1 out of context.
As St. Thomas Aquinas put it, "Parvus error in initio magnus erit in fine.” (“Small error in the beginning; large [error] will be in the end”). From the beginning error of believing a person is what they do, the concluding error is condemnation of a sin = condemning a person. A person may have a job as an accountant, but that does not make the person an accountant and a person may have a same sex attraction, but that does not make the person a homosexual. The Church believes that a person is more than their actions or ethnicity—and to reduce them to their behavior is to treat them as less than human.
In terms of Catholic teaching, the person is primarily a child of God. The individual may be ignorant of that fact. The person may reject that fact. The person may accept that fact. But regardless of what the individual does with that information, the fact remains that he or she is a child of God and however they are treated must reflect this fact. Because of this, the Catholic Church never allows us to turn our backs on the sinners, the poor or anyone else—we’re not allowed to write off anyone as irredeemable.
But the fact that we, as Christians, cannot write off anyone as irredeemable has one very important fact that follows from it—every person is in need of redemption. That indicates that we are at odds with God in how we live to some extent. When we act in a way which is contrary to how God calls us to live, that needs to change. Living contrary to God’s call blocks us from Our Lord's redemption, and such behavior must be abandoned if we would be saved. People who know what the truth is can offer correction, just as the person who teaches can offer a student correction when the student gets a wrong answer. That’s not being judgmental. Consider this excerpt from a Socratic dialogue by Peter Kreeft (one that does not deserve to be in obscurity):
Libby: You sound so damned sure of yourself, so dogmatic, so judgmental! Your namesake[*] said, “Judge not.” But you don’t dig that soft stuff, do you?
‘Isa: What do you think Jesus meant when he said “judge not”? Do you think he meant “don’t judge deeds, don’t believe the Commandments, don’t morally discriminate a just war from an unjust war or a hero from a bully”? He couldn’t have meant that. He meant “don’t claim to judge motives and hearts, which only God can see.” I can judge your deeds, because I can see them. I can’t judge what your motives are, because I can’t see that.
Libby: Then stop being so judgmental about that, at least.
‘Isa: But I can judge what your motives ought to be—just as you’re doing, when you judge “judgmentalism”.
—Peter Kreeft, A Refutation of Moral Relativism: Interviews with an Absolutist
(San Francisco: Ignatius Press, 1999), 108.
So the Christian teaching is not “homophobic” or “anti-woman” (two popular epithets today). Rather the teaching is concerned with letting people know how their lives estrange them from God and what they must do to be saved. It’s not a hatred. It’s a case of viewing a person as being worth the effort to save—worthy of receiving our love because God loves them.
Sure, you’ll find Christians who are judgmental and hateful. You’ll also find atheists and Buddhists who are judgmental and hateful. But the Christian who actually hates another person because of their sins is not acting as God commands them to act. They are not acting as the Church commands them to act. I think people forget that. Yes, in the Middle Ages, punishments that we now see as barbaric were seen as normal. But even then, the person was not reduced to the evil they did. Even when the evil done resulted in Capital Punishment, the Church was still concerned for the salvation of the person—to bring them back to right relationship to God before they died.
But what happens when a person refuses to be brought back into right relationship with God? We certainly cannot say “Oh well, might as well go ahead and do it then.” We cannot allow people to redefine their action as “good.” But we can try to show love in pointing out that this action is harmful to a person based on what God wants them to be—because trying to encourage a person to abandon a harmful action is an act of love, not an act of hatred.
[*] The Arabic form of “Jesus” is ‘Isa. Hence the reference to “Your namesake” in the quote from Peter Kreeft.