Oh how I hate this phrase. It is so full of hypocrisy and judgement. Let me explain:
By telling someone that you love them, but that you hate what they do, you are, in effect, passing judgement. You must necessarily put yourself in a position above them to be in a place where you can call out another individual's actions and label them as "sin." The fact is, we are all sinners. Just because someone sins differently than me, doesn't give me the right to make any judgement on their different way of sinning. I do not know the circumstances. I do not know the mind of God. Murdering is a sin, yet God himself commanded it multiple times. "Now Nephi, I love you, but I hate that you are disappointing God by killing another human being (Laban). That is a sin, and I hate it."
If everyone is a sinner (and therefore all men and women commit sin), let's not say "the sinner" and "the sin" as if the person speaking is in someway immune to these things. Why don't we instead adopt the phrase, "love everyone, love God." Sound familiar? These were the two great commandments that Christ taught. If we love God, our personal choices and actions will attest to that ("by their fruits ye shall know them"). Individually, we learn to love obedience to God and hate to disappoint him. But this in no way give us the right to judge and say to another "I love you, but hate that you disappoint God." Who are we to tell someone that God is disappointed with them?
Perhaps the initial use of this phrase was well-intentioned. If this phrase was solely applied to one's self, we are, in effect, saying, "I love myself as a valued son/daughter of God, I hate that sin so easily besets me. I hope to learn to detest sin, for I love God." But the minute we use this same phrase in reference to someone other than ourselves, we enter dangerous ground.
We should love people (all people) for who they are, not in spite of who they are. Christ commanded us to love one another. It is that simple. He didn't say "love your neighbor even though they sin and are disappointed me by their actions. Just be the better person my making sure they know they are sinning. Oh and tell them you love them too." I think it is time we all come down from our pedestals. God is no respecter of persons and we are tasked with working out our own salvation with fear and trembling, not with working out another's. That's Christ's job.