You have to hate someone to want to hurt them with lies as insincere talk brings nothing but ruin.
Out of pride comes envy. Out of envy comes hate. Out of hate comes slander. And it’s always in some way or another to enhance the slanderer’s person or position.
You cannot be sincere if you say you like chocolate when you hate it. You cannot be sincere when you compliment someone but deep inside you detest him or her. You cannot be sincere when you apologize just for the sake of disarming the person that you offended, with the motive of future revenge.