Which type of karma?
There is something like karma that I can accept. Then there is the popular version. The two are diametrically opposed.
The popular version of karma is that we are rewarded or punished in this life for the sins and good deeds of lives past. The world is fundamentally fair, we just don't see in this life the full causes.
This is a theory that is very comforting for the powers that be, and is good for soothing the downtrodden masses. Who after all must deserve a little downtrodding, else they would not be in the downtrodden masses! But I can't buy it.
Then there is another version of karma. It is the idea that your actions establish patterns that the world reacts to. Your actions create ongoing patterns with their own consequences. This isn't a theory that says that what happens is based on any cosmic fairness. Just patterns. The world is how it is because that is a stable pattern, and not out of any cosmic fairness.
This is a theory which the rulers don't like so much. It says that they rule because someone somewhere decided to enforce power and managed to succeed and hold it. Armed with a theory like this, the downtrodden masses are liable to think, "Hey, we are downtrodden because we accept downtrodding. Doing something about it may be dangerous, etc. But it is up to us to do something about it if we want to avoid remaining downtrodden!"
But from my (admittedly limited) reading of Eastern religions, this interpretation of karma is in perfect accord with what they say. (But note that the explicit goal of Buddhism is to try to break all of the patterns you are involve with. I do not think this possible, nor do I think that attempting it is good. But then again I am not a Buddhist.)
BTW karma is not just an Eastern concept. While Western religions may not believe in life after life with karma ongoing, karma is the concept encapsulated in popular sayings like, "You reap what you sow", "What goes around, comes around", "Do unto others as you would have them do unto you", and so on.
Cheers,
Ben