I believe your Axiom of Causality is seriously flawed. Let's unpack it and see why.

1. Nothing takes place without a cause.
This is not true. According to science, there are events which do not have sufficient causes. Some events are undetermined. If you were to run our world backwards to some prior point in time (but after it's initial state) and then let it run forward again, you would eventually evolve a world which would differ from our present one. That's because the world will always be reaching forks where it could go in multiple different directions. And we cannot predict in advance, even in principle, which direction it will take.

2. The magnitude of the effect is proportional to the magnitude of the cause.
This is also not true. The very notion of an explosion (an exothermic process) is a process which produces a net energy gain. The heat of a match is much less than the heat of the dynamite explosion it triggers.

3. Every action has an equal and opposite reaction.
This is true in reference to physical/chemical processes. But it is a fundamental category error to extend this notion into the domain of ethical reasoning. Newtonian mechanics says nothing about karma. Neither are the philosophical reasons in favor of karma persuasive.

I'm not sure I agree. It seems to me that actions are causally connected sequences of states. The action of throwing a fastball starts with the pitcher's windup and ends when the ball comes to rest in the catcher's mit. An action is an incremental set of change to the state of an object over time. I'm having a hard time imagining instantaneous actions.

What do you think?