It's upon the individual to not let the personal hatred cause him to be unjust (to others) as Allāh stated:

O you who believe! Stand out firmly for Allah and be witnesses for justice and let not your hatred of people make you be unjust. [Sūrah Al-Māidah(5):8]

This is (true) justice, that the person judges with justice (in all affairs); This is whether it is for himself and/or other than himself, out of fear of Allāh (and His punishment for not being just).