We can love people without embracing their sin. No person, made in the image of God, is defined by their sin. To "despise" as person requires hate in one's heart - the very antithesis of Christian love. 

Now, of course, we must avoid judging the hearts of others and condemning them. However, we should encourage those who are living objectively sinful lives to repentance, as one sinner to another sinner, not judging culpability. To do so is a spiritual work of mercy. 

Did Paul "hate" the Galatians when he wrote?

"The impulses of nature and the impulses of the spirit are at war with one another .... It is easy to see what effects proceed from corrupt nature; they are such things as adultery, impurity, incontinence, luxury,  idolatry, witchcraft, feuds, quarrels, jealousies, outbursts of anger, rivalries, dissensions, factions, spite, murder, drunkenness, and debauchery. I warn you, as I have warned you before, that those who live in such a way will not inherit God’s kingdom."