If he wants good mental health he does. Hating will sprout a root of bitterness, and a root of bitterness poisons everything in life until it is removed, often through difficult psychoanalysis.
A few years after my divorce, I was led to the Lord by a friend. Shortly after, I took an inventory of myself and confessed my bitterness, realizing that it was based in fear.
I didn't have it in me to forgive because I hated her so much. But I knew it was God's will for me to do exactly that. So I confessed to him that I did not have it in me to forgive, but I acknowledged His will and ask Him to give me that ability. next, I started to pray for her, asking God to bless her. To make a long story short, I found that ability to forgive, and was delivered from the bitterness. In the end, she ended up getting saved too. She now goes to the same church I go to, and the kicker is that she has asked my current wife to be her spiritual mentor.
God is so awesome!