I feel sorry for your that your dad did not have the guts or interest to stand up for you. Mine always did and so I do for my daughter. Seems to be a bit of an issue with social development.
If you think, that this incident did not carve a long lasting impression then you must seriously lack a sense of fairness and just -- maybe linked to your own scars (see above).
I am lost of what you try to say here: When bad things happened in the woods 50 years ago, we consider them ok? Why not go back to a good old flaying? I mean, THAT would teach them -- right?
Cancer is a big issue. War is a big issue.
A 6 year old in wrong clothes is NOTHING. Not in any culture or any country. And don't say "Thailand", there are actually excellent schools in Thailand and very educated people.
Sure, do that to my kid and there would be definitely implications.
If there is any problem with a student, big or small, the CALL THE PARENTS and hold them accountable. If you touch a 6 year old (unless there is immediate danger to prevent), then you are unfit for any job, but especially as a teacher.
Ask yourself a simple question: Would they have dared doing the same on a 16 year old student (not too wimpy)? I guess not and this demonstrates all what went wrong here: its pure bullying and abuse of power.