Is it possible to define various level for safety?

Basically no. To a language , saving your password in a password manager looks exactly the same as leaking it to a pastebin.

The reason unsafe is such a critical difference is that UB means you can't trust what you see. If you get it wrong and hit UB, you might have logging that "shouldn't" have happened, might be missing logging that "should" have happened, might be running code under conditions that you "checked" etc.

So long as you avoid UB, you can have telemetry, you can do code analysis, etc.