I have been wondering for some time now why causality is a prerequisite for every "good theory" all the way from classical mechanics, to QM, even in QFT the correlators for spacelike separated interactions cancel out. Now, since we usually take make a general theory and then usually simplify, consider special cases, etc, why not assume a general theory at the quantum level of which causality is just a special case ? To clarify my thoughts, my question arises from debates with colleagues who said it might just be axiomatic since we have not seen any evidence to the contrary. However, the same holds for tunneling, so why not assume a more general theory in which non-causal interactions are simply exponentially suppressed as we approach macroscopic scales and build a theory from that ? What is the fundamental argument for insisting on causality ?