For one, you now know exactly where the memory unsafe code is, rather than a cloud of suspicion hanging over every line of the codebase.
I think Rust strikes a perfect balance between a safe default and, as you say, "localized unsafety". Said localized unsafety is however only localized as long as you're "doing it right". I would absolutely not trust an LLM to do it right for hundreds of thousands of lines of translated code. This is insane.
I'm writing this as someone who doesn't even really like Rust; I'd probably prefer to write Zig! But those unsafe blocks definitely buy you something.
I don't see how this is any different from every line trailing with a comment of the form "FIXME: This line might be wrong".
And I say this as something of a Rust fanboy. I love the way unsafe blocks work, and the "locality of danger" they give you. But that all goes out the window if there's a gazillion haphazardly written such blocks.