"Just use clone" seems like reasonable advice to give people on day 1 or week 1. I guess the hazard there is that they might end up writing `fn foo(s: String)` everywhere instead of `fn foo(s: &str)`, but they can gradually learn the better thing through case-by-case feedback, and correcting this is usually a small change at each callsite rather than a total program rewrite.

On the other hand "just use Arc" is definitely smelly advice. I think going down that route, a new Rust programmer is likely to try to do something that really won't ever compile, and wind up really frustrated. Maybe we can distinguish this often-really-bad advice from the other mostly-ok-at-first advice?