Why does the Bible tell us to love our enemies and not repay evil with evil?

Anonymous
I strongly disagree with the teaching. People must get what they deserve. When a person does good to me, I’ll do good back to that person in return. If they do bad to me, I do bad to that person in return. A person must reap what they sow. Good things are to happen to good people and evil things are to happen to evil people. Also, I hate pacifism because it’s useless. If I need to defend myself, I’m going to do it; I do what’s right for me and God.
Why does the Bible tell us to love our enemies and not repay evil with evil?
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