No, karma is a crutch for people who can't handle the idea or possibility of life being unfair. It's weird how belief in an unproven, magical, all-powerful god is criticized and made fun of but so many people believe in an unproven, magical force(karma) that punishes people. They're both unproven, supernatural things.

As a stance of mind it is.

No

Don’t know.

From Conversations with God book 1 by Neale Donald Walsch:

No, there is no such thing as karmic debt—not in the sense that you mean in this question. A debt is something that must or should be repaid.

You are not obligated to do anything.

Still, there are certain things that you want to do; choose to experience. And some of these choices hinge on—the desire for them has been created by—what you have experienced before.

nah there is only randomness - some people will get back what they put out into the world and some people will not, nobody is keeping score (or if they are, the score is ultimately meaningless)

No, but revenge is.