Karma is often perceived as an ultimate justice system that rectifies perceived wrongs, where actions are recorded as good, or punished as bad. A justice system where no human intention or action is needed is very appealing to the human condition.
Karma appeals to our desire for justice, and brings relief and settles the minds regarding injustices that we cannot right. However this relief can come with unintended consequences, such as promoting complacency and a sense of inaction. To truly have a fair justice system, it requires active engagement from individuals who use their own reasoning and critical thinking skills. In the absence of a perceived overseer or ultimate justice system, it becomes all the more crucial for individuals to take responsibility for their own reasoning and self-corrective processes.
If we believe that justice comes from a magical force or a god's punishment or blessing, we are less likely to take that on ourselves, and truly value the importance of the work required to maintain and grow a just system.
Karma can also be seen as a purely internal and humanistic force, a word used to describe actions taken from human reciprocity and memory, which is not superstitious. I find this definition to be relatively rare, but it's worth mentioning that the above does not apply to it.