If Karma was a real thing (or God) it wouldn’t be usually. Just the injustice in this world is enough to disprove the false-god Karma.
Karma is not a god. Karma is the way things work, and even if it doesn’t seem like it, there is no way of avoiding God’s justice. Just because you don’t always get to see it doesn’t mean it’s not there.
Why do you think you are admonished to do onto others as you would have them do onto you. Do you think those were just idle words? A mere suggestion?