"According to my way of thinking, however, the best way to learn to be prudent is to realize just how imprudent one can be..."
According to my way of thinking I really couldn't care less about your way of thinking. I think the best way to learn is to look at the mistakes dumb people make; its a pity I don't know you.
It is a pity. It is truly amazing, that not only do you let someone take advantage of you. But then you defend your far from stellar actions. I'm not you enemy Avenger, look inward. That part of you that is feeling shame for not acting. It might hold the clue.
Avenger: noun 2 : to exact satisfaction for (a wrong) by punishing the wrongdoer
Irony: 2 a : the use of words to express something other than and especially the opposite of the literal meaning
Tackling that guy would only have gotten you arrested, and I am sure the last thing you need is an arrest record.
This situation was ambiguous enough, that you did the reasonable thing: you did alert the guard, who should have been the one to confront this guy and call the police.