While I agree that this is a teachable moment, it doesn't have to personally attack the hiker.  This debate goes on at 14ers dot com all the time and many make the mistake of coming off as superior and judgmental toward others.  

The upshot is that everyone has their own notions of personal safety and risk.  The instructor would be better served to take a tone like "a signaling device would greatly assist the rescuers in the event the hiker unexpectedly becomes lost."  Expecting every person to buy a SPOT tracker by shaming them is naïve at best.