*nod* Rust's "make costs explicit" design does have a bit of a problem with encouraging premature optimization where something like Python would encourage sloppiness.
I agree... you need discipline either way. It's just easier to wind up not realizing that you don't need to spend so much time on up-front optimization with Rust to produce a perfectly serviceable program. (Especially if you haven't internalized the whole "fearless refactoring" angle.)