He's very well read, which is respectable, but I find myself disagreeing with a lot of what he has to say about Christian conduct generally. I have talked with him before.
I find it likely he will comment on this soon. I do not think it wise to bring it up this publicly (no offense to you, of course), but perhaps it may serve as an opportunity to further discuss the nature of God's character and how we are called to treat others.
That being said, I agree that hatred does not have much place in Christian conduct. There are times where we must be rough or harsh, but I have never found such actions or commands concerning that to be born out of hatred for sinners; I have always understood it as the opposite, in fact, for various reasons which I will not elaborate on immediately, and I have not seen anything to indicate hatred in them. And seeing the way human hatred twists the world, I do not wish to take part in similar feelings.
Regardless, though, Paul wrote this:
Let all that you do be done in love. (1 Corinthians 16:14)
Therefore, doing anything out of hatred is already excluded from the equation.
Best wishes to you and him.