Earlier quoted context omitted.
Not to put too fine a point on it, but "side effects" != mutation. Also: The level of control offered by Rust comes at a steep cost compared to GC'd languages.
I am relatively new to rust, but motivated to learn it right now. Could you elaborate on what the cost compared to garbage collected languages is?
1. There's a mental cost on the programmer. You have to learn all the ins and outs of things like the "borrow checker" (a Rust concept) and it's on you to understand the rules and how to use them
2. It can slow down compile time. As your program gets bigger, the compiler is doing more work to check that it's valid code, so that will slow you down.