St. Augustine has this wonderful passage from one of his sermons:
So, of course, say to your friend, who wants to make you the enemy of your friend--speak to him and so to say massage his aching spirit with a soothing liniment--say to him: "Why do you want me to be his enemy?" "Because he's my enemy," he answers. "So you want me to be your enemy's enemy? What I ought to be the enemy of is your vice. This one you want to make me the enemy of is a human being. You have another enemy, whose enemy I ought to be if I am your friend." "Who is the other enemy of mine?" he answers. "Your vice." "What's my vice?" he asks. "The hatred you hate your friend with." So be like a doctor. A doctor doesn't love the sick person if he doesn't hate the sickness. To set the sick free, he persecutes the fever. Don't love the vices of your friends if you love your friends." (Sermon 49, Section 6, from The Works of Saint Augustine: Essential Sermons, translated by Edmund Hill, O.P., edited by Boniface Ramsey, p. 60).
Too often today we see people dismiss as false or hypocritical the idea of "hate the sin, love the sinner." We see this attitude lodged against the Church and her followers with regards to the Church's teachings on sexual morality. However, Augustine reminds us that real love desires to bring our loved ones into conformity with the truth, for the benefit of their physical and spiritual health. To condone misdeeds is to make our love for them a superficial and self-serving thing. But we also have to remember that as Christians sometimes we forget to make the vice our enemy, not the human being. We should remember this when we speak of people like the late Senator Edward Kennedy. He worked terrible evil in his promotion of abortion in this country, and we must not fail to speak of it as a terrible evil. But we must also loudly speak of our desire and hope for the salvation of his soul, for he was a child of God. I think of some of the anger some feel about illegal immigration. We can condemn illegal immigration while still acknowledging the humanity of the person. As usual, Augustine challenges us, regardless of our political or religious partisanship.