This is such a provincial attitude, wanting to prohibit people from using perfectly normal names like Amélie or Jürgen or Ольга to log in just because you as a programmer can't be bothered to deal with a numerical ID instead.

You can have such names as Amélie or Jürgen or Ольга or 𠮷野 or 鎮󠄁 and have them displayed on account management screens, you just can't use it for login IDs because there are no guarantees that those blobs can be reproduced in the future or be consistent with what it was at time of entry.

Unicode is that bad.

No, it's an entirely practical attitude, unlike outrage culture.