“Jets” are the proverbial “Sufficiently Smart Compiler.” The seal between a core of Maxwellian purity and the world of filthy expedient compromises which lies outside must be absolutely perfect – like the seal on the airlock of a multi-generational starship. In fact, building the airlock at all is a terrible idea. Anyone who whines about being welded into the hull doesn’t belong on the journey.
Think of every high level language with a C FFI you’ve used. Having the FFI is not harmless. It colors the programmer’s thoughts. It destroys the Master-Of-All-I-Survey majesty of the entire system. Another way must be found.