I have mentioned here at least once the principle of getting someone to like you by asking them to do a favor for you, rather than by doing a favor for them. You might remember the story of Ben Franklin getting a political opponent to lend him a difficult-to-obtain book, and that creating a relationship of cooperation.
It occurs to me this morning that this likely occurs with hatred as well. If you do something mean to person, such as throwing them under the bus to colleagues, or losing your temper, then they must be a bad person, because you, a good person, would not otherwise treat someone that way. It likely intensifies or solidifies as we go forward.
If you treat people well, you will like them better. They might not be any better, but you will think so. If you treat people poorly, you will learn to hate them. You might make them worse people by doing so, certainly, yet even if they remain unaffected, you will perceive them as worse.