If you are a professing Christian chances are pretty high that you have uttered the phrase "hate the sin, love the sinner" at one point or another. At the least you have probably heard it tossed around here and there.
The sentiment is fairly straightforward. It conveys the idea that you can entirely disagree with, and be at odds with someone's behavior, while still caring deeply about them. The idea itself is fine. We really are at odds with a lot of dangerous behavioral stuff in this life. Hopefully we're more at odds with the junk in our own closet rather than someone else's. The problem with this idea isn't that it's untrue. It's that we don't actually mean it.
Generally whatever particular sin issue is driving the conversation usually dominates said conversation. This leaves little room for lovingly engaging people who might be neck deep in the issue at hand. God is amazingly loving, and forgiving, but how can you demonstrate that to someone if you are too busy telling them how much God hates what they're doing. It's like trying to give someone a brand new car by running them over with it. Or giving someone dying of thirst a drink by tossing them in a lake.
Christian, you are the face of God to this world. You are Jesus with skin on. Often people will respond to God in accordance to how you respond to them. Not always, but many times.
Also, you need God too. We all do. "Hate the sin, love the sinner" is a fine description of how God feels about the situation, but it's a pretty crappy summation of Christian human reaction to sin.
God does hate sin. He hates all sin. He is completely good like that. God does love sinners. He loves all sinners. ALL OF US. He is completely good like that. But I have yet to meet the Christian who hates all sin equally and loves all sinners equally, and that certainly includes myself.
No, we pick sins that are obvious and we hammer them, leaving those trapped in that sin beaten and broken like some old rusty nail. Never mind that Jesus allowed himself to be beaten, battered, and nailed for them. All the while we ignore our pet sins and keep them in our most secret places. Even the villainous religious leaders from John chapter 8 had the good sense not to throw stones because of their failures. Would we? I have met a lot of people who went looking for God at some point in their life and wound up battered and bruised by the stones thrown their way.
I've spent over a decade reaching out to college students. I've had hundreds of conversations with non Christians. It is amazing how many people are turned away from Christianity, not by Jesus, but by the people who represent him. In their eyes we hate the sinner, but we love to talk about their sin.