How do you reconcile the fact that good requires evil to defend itself

I’ll admit I find it hard to accept a moral system which says that Martin Luther King and Bull Connor were acting with equal morality; both men were defending what they saw as good against what they saw as evil. The system seems to be saying there is no such thing as good or evil.

A person can do many good deeds. Evil does not define a person’s ability to be good. It only defines partly good when it has to be confronted.

Just because you believe something to be good doesn’t mean it actually is good; just because you believe something to be evil doesn’t mean it actually is evil.

What do you depend on then, if not your personal beliefs?