A nice historical perspective relating to present use of flipping the bird.  As you say, the marines shouting "fuck you" emboldened them in the face of being attacked to take action that saved lives.

Ms. Kent by her own account felt "bullied".  Were Senators Hirono and Schatz the bullies, because her bird flipping was right between their heads?  Or maybe it was meant to flip the bird to Rep. Tulsi Gabbard, a fellow progressive who spoke of aloha in her nominatinating speech for Bernie Sanders?  Makes me wonder.

One thing for sure...flipping the bird casually can be life- threatening (e.g., roadways) and definitely not life-saving.