First I would like to say Bravo to the OP for having the courage to ask such daring questions!! And now, my two cents.

Personally, I'm an atheist and don't believe in any sort of metaphysical "force" like Karma. I think the basic principle of it is true though. Do good and you will receive good, do bad and you will receive bad. You reap what you sow. But, as you may or may not have pointed out, there really is no absolute good/bad or right/wrong. And my general belief is that people mostly do whatever they want anyway. It just so happens that some of those actions are what a specific society/religion/government/parents, etc consider to be good or bad. If tomorrow we woke up and suddenly everything that was considered good was now considered bad I think we would all still behave pretty consistently with our personality thus far. So what's the point of it? The existentialist in me says that the point is to live a life that is meaningful to you. A life with no principles, no concept of right/wrong is essentially a life with no values. With no values, what is there to find meaning and worth in? Also, with the idea of punishment, ethics does not necessarily have to be consequence driven. It could be argued that what's good is good regardless of what the consequences may be. This isn't a view I hold, but some do.

I think webgoji's suggesstion of imposing your own will on others is circular. If there really are no consequences, then what would be the point of imposing your own will on others? There wouldn't be any because you essentially have no values, so why would you value your own will?