I really was talking about serious/ complicated systems, where you want some consistency in the components it is made of even if a particular case could just use an incremental id. I my view, you don't spend the mental energy on switching between models. I have just adjusted/ rewritten a part of the system, where we for historical reasons used logins instead of UUIDs. By using logins in this particular case, we had subtle bugs that wouldn't occur with UUIDs. It would never have happened, had we used UUIDs everywhere from the start. Those already have standard validation functions and you don't have to think about stuff that really isn't your business problem. We are also talking engineering days thrown out of the window just for the change from logins to UUIDs later on. I don't think you waste so much time copy&pasting stuff.

I guess, we arrive at the same conclusion but have our differences about the ways leading to it. We both want to focus on business problems as much as possible.