I get what you're saying, but I think the issue with optional memory safety features is that it's hard to be sure you're using it in all the places and hard to maintain that when someone can add a new allocation in the future, etc. It's certainly doable, and maybe some static analysis tools out there can prove it's all okay.

Whereas with Rust, it's built from the ground up to prove exactly that, plus other things like no memory being shared between threads by accident etc. Rust makes it difficult and obvious to do the wrong thing, rather than that being the default.