The problem is that there are so many functions that unnecessarily take `&str` rather than `&[u8]` because the expectation is that textual things should use `&str`.

So you naturally write another one of these functions that takes a `&str` so that it can pass to another function that only accepts `&str`.

Fundamentally no one actually requires validation (ie, walking over the string an extra time up front), we're just making it part of the contract because something else has made it part of the contract.