You're allowed to disagree. It doesn't mean you're right
To me it's a situational thing, as is most stuff. I don't know the conditions you were flying in, what day it was, the location you were in precisely, whether there was active gliding, whether your instructor had in fact called portmoak on the phone before departure.
I've been gliding a couple of times, I don't have the patience for it
I have nothing to prove, but you seem to want to.
I mislike this attitude that "this is incorrect, that is not the right way to do it. It must be done like that" pilots seem to spout, particularly inexperienced ones and grouchy Captains.
I hear loads of pilots spout off about what's right and what's wrong and in most situations there is merely what happened at the time was decided correct for the given conditions.
Flying through a DZ while drops were going on and not speaking to anyone on the radio, is unquestionably not a grey area, it was extremely unwise.
Doing spins in a Cessna, 10 miles from a gliding site at 5000ft is totally different. If you can't see why then you need to think about your approach to airmanship.