Just shut up and do something about it, is a great way for nothing to ever get done about anything. It's essentially gaslighting.
"Whining", as you put it, is a way of passing on information, keeping it in the public consciousness, letting others know what to avoid who don't know that these Cracker Jacks have been trimmed before they were sent to the TPG's.
Very little of any consequence has ever been done, without a great deal of "whining" and hand-wringing involved.
Imagine if your buddy in the scenario you gave, identified the mugger to the police, had plenty of evidence to back it up and nothing ever got done about it.
Then that mugger kept on robbing your buddy over and over and over again. Identified every time, and nothing is ever done. Short of your buddy going full vigilante, at what point does he shut up and just learn to live with his daily muggings?
At what point do you point your finger at your buddy, tell him to shut his big fat whiny mouth and go "Death Wish", or figure out some way to reform the police force in his locale, and everything systemically wrong with it.............but do it quietly and without disturbing anyone else's sleep, or forum reading habits?