Haha, what is this, the 90s?

Assembled instructions aren't even the lowest non-hardware stage in instruction execution. There's proprietary microcode sitting a level below your typical x86 ISA.

And even then, what if—God forbid—the hardware has errata. A line has to be drawn somewhere between trusting that what you write is logically correct at all stages below it. If someone is unable to trust that the environment they wrote code for works, they better start learning how to create PCBs and writing for FPGAs.