Personally, I think there is some merit in respecting people's expectation of privacy even when in a public place. So, while I am primarily a people shooter, I don't engage in it as an aggressive pursuit like some self-centered predatory Paparazzi ... Magnum shooter or not, my first instinct would be to bitch slap someone like that to his knees, then claim "I was startled and in fear of my life"
The notion that there is some "higher purpose" like recording "humanity in all it's glory" isn't the same as a duffer wading into the gene pool and taking a self-gratification pee.
However, if people make a spectacle of themselves, or are at a place or event where there is some expectation of being photographed, that's a different story.
I wouldn't consider those shots at a Parade or any similar gathering to be an invasion of privacy. Portrait work isn't the same either ... there's an expected purpose. Same for all my candid wedding work
There is a line there, and I know I can cross it, but tend not to out of respect for that very humanity that others think is their private hunting ground.
I've done okay at street stuff, and I truly think it is the domain of the Leica M ... not to be sneeky, but to go unnoticed so as to not disturb the flow of life around me.
Different strokes for different folks.