Nick... this is not exactly the level of discussion I was hoping for, but I will respond.
In science, the "action reaction" language is used to express Newton's third law of motion. It doesn't contain the lesson you want it to.
Newton's third law applies to a bug hitting a windshield. This means that the bug puts the same force on the car that the car puts on the bug. However balanced this seems, the results are far from equal.
The bug comes to an untimely end while the car is slowed an imperceptible amount.
The driver who started the process might never even know about the individual life she snuffed out. Although she has one life to give for the hundreds she might take an evening of driving, the consequence is rarely more than the need to push the windshield washer button.
I don't think the scientific principle of Newton's third law has anything to do with the religious concept of Karma.