That's trivially untrue. Nothing about turing machines or lambda calculus requires temporal unsafety. Even this example wouldn't exist if the compiler rejected covariant lifetimes. You already know this of course, so I'm not going to keep beating that dead horse.

The obvious follow-up is to find a minimal set of rules that allow us to express what we want without permitting temporal unsafety. The borrow checker is one set of fairly minimal rules that works pretty damn well. Alternatively you could define away the unsafety by giving it semantics, like fil-C does.