Why are you still moping about this 40 years later?
Even just one particularly nasty or traumatic incident can stick. Or a long series of events.
I've been dealing with a therapist... a particularly good one... for quite awhile now, and it's surprised me as to just how many issues I have that eventually trace all the way back to school and bullying, as I was a frequent target, as was my closest friend.
And there absolutely are certain events that REALLY stuck and led to me being entirely paranoid around people. Like there was one time when my friend and I were walking down some stairs, at a school event, with me in front and my friend directly behind me a couple of stairs back. A particular snot of a bully decided that holy heck it'd be SO darned fun to shove my friend down the stairs. He shoved my friend, who slammed into me with all his weight, hard. Fortunately for both of us, while my upper body strength is terrible, I have extremely strong legs, and could absorb the hit without going down. If that hadnt been the case, either or both of us could have broken our necks or something falling down those stairs. I went after the bully after that and did... something... he never bothered us again. But that ONE incident really messed me up. It's one of my strongest memories from school, and ever since then I've tended to automatically view absolutely everyone (that isnt a friend or family member) as a possible threat.
It also gave me a VERY heavy distrust, and even heavier dislike, of children in general. Absolutely cant stand them. That hasnt faded even slightly in the 25 years or so since that happened.
And of course the teachers were generally useless for dealing with any of that. Somehow they always managed to be absent. They may as well have not even been there. It always seemed ridiculous to me, being in a place that was a contained zone for kids, supposedly safe, yet the adults just sorta blinked out of existence all the bloody time if lessons werent happening. I dont exactly have very good opinions on the education system as a result.
That event isnt the only one, but it comes to mind very frequently even after all that time. So I can understand how someone would carry something like that just sorta forever.