Aren't there two questions here?
1. What is the absolute minimum that all students should be exposed to,
and
2. what would it be a good idea to show and teach the students during their training?
The answer to the first Q is what should be in the (mandatory) syllabus, and the answer to the second Q is what the instructor can choose to show the student if he/she is so inclined and feels the student would benefit from it.
I got to spin the C172 during my PPL training and am really grateful for that; apart from it all being great fun
it makes me more confident when practicing stalls on my own, knowing if I screw it all up and end up in a spin I can recover from it. That the C172 is more reluctant to spin than even the even the most cautious instructor is no drawback IMHO; if you're going to fly a non-aerobatic aircraft, shouldn't you learn recovery in such an aircraft? And you
can get the C172 to spin with a little effort; been there done that...
But if neither the student nor the instructor is happy about it, maybe it's better not to do it...