> what's the justification of not using a memory-safe language

Use Go, Java or Fil-C, and memory safety is achieved at the expense of runtime performance. Tracing garbage collectors make your programs run slower and use more RAM.

With Rust you pay with complexity. Rust has new, weird syntax (lifetimes, HRTB, etc) and invisible borrow checker state that you've gotta understand and keep track of while programming. Rust is a painful language to learn, because lots of seemingly valid programs won't pass the borrow checker. And it takes awhile to internalise those rules.

I personally think the headache of rust is worth it. But I can totally understand why people come to the opposite conclusion.

> because lots of seemingly valid programs won't pass the borrow checker

Some straight-up valid programs as well