I’m sorry, but I thought I made it clear above. Let me try to be brief this time.

Can one person hate another?
Yes

Is it right to do so?
No, if it’s a hatred related to their physical self; like hating a person because they  are ‘black’ or ‘french’ or ‘of Jewish decent’, but hating them because of who they choose to be, then of course. If someone chooses to be a mass murderer then yes, you hate him for his choices. We don’t care if he is an American or Muslim, where most serial killers are from, we only care about who the person is.

Does that hatred remove them from the pale of mercy, good and fair behaviour?
No, based on what i explained above. So if someone is an evil person, I would hate him for his evil, but that doesn’t mean I won’t try to stop him from that