As it is the meaning of a safe hint is to be intuited by the recipient.
Yes. That's not a bug.
I don't understand the point of hypothetical arguments about whether a
safe flag might be useful. We already know the answer: Many of the
largest web services in the world already have one. Youtube puts
theirs right on the home page.
All this does is to provide a consistent interface to the existing
feature, and some operational flexibility to environments like schools
and corporate networks where the person sitting at the browser isn't
the one who sets the content policy.
R's,
John