I love philosophical discussion.
If amateur radio is solely the art of bi-directional communication (me to you, through a medium, battling noise of all sorts, you back to me, with encoding of meaning, followed by understanding and compliance), then what would we call building repeaters (something that I compare to NCIS' Gibbs building his boat in the basement; I find beauty in rebuilding 70s vintage stock two-way radio systems that use professional equipment for amateur use... just my weirdness), or antennas, restoring an abused Collins S-Line, or just homebrewing a QRP rig simply for the joy of doing so?
And, we have the folks who I wonder about, who are DSTAR, Echolink, or IRLP enthusiasts (I've played with all 3 and they weren't for me)? They are no less hams than we are, even if they might not even be using a radio for their QSO. (I draw the line at eQSLs, though. LOL.)
The only prerequisite to being an amateur radio operator is having a license. I'd even extend that to someone who's actively studying for a license. They are immersed in the hobby, too.