I don't know that clones are problems in and of themselves rather than what they do behind the scenes: allocations. Cloning an Rc is completely innocent, cloning a HashMap<String, Vec<String>> is deadly in a way you may not expect if you're used to shallow-copying hashmaps (or even deep-copying them).
And it's true that if you think of allocations as being no big deal unless you're aiming for very high performance, your Rust is going to be slow (also your C++ and your C).
And it's true that if you think of allocations as being no big deal unless you're aiming for very high performance, your Rust is going to be slow (also your C++ and your C).