There is no rule about pinging someone to a post just because you mention them.
Freepers enforce the rule of pinging someone when you post about them, especially bad mouthing them and attacking them.
I doubt management wants a person destroyed by someone attacking them around the threads with him never even knowing it.
That would be part of holding grudges and dragging baggage around.
You like the concept of that practice?
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There may not be a written rule, but it is considered common courtesy to ping someone if they are mentioned in one's post.