Well, you
were thinking, anyway, for a brief, shining moment. I misdoubt you will again, and for longer next time -- once you start to get a taste for the habit, it's all but impossible to kick, not least because you don't want to.
Now I have to come clean: I gave you a trick question, asking you to define a function which in fact is trivial. Do you know Lisp? Never mind, it's simple enough, not least because we can cheat by assuming the definition of 'legitimacy' -- here, I'll give it to you in Lisp, thus:
(defun mob-legitimate-p (&rest args)
nil)
Let's assume I feel, for whatever reason, that you done me wrong. Let us further assume I find it meet to express my resulting dismay by first blacking your eye and splitting your lip, and then aiming a loaded shotgun at your brisket and demanding that you put right my grievance, in the precise fashion I see fit, lest I splatter your thorax across the opposite wall.
Now, leave aside the question of whether you've given me cause for grievance, which you'll note was nowhere mentioned in your homework assignment. While I'm aiming that shotgun at your chest, how legitimate do you think you'll regard my grievance? How does it affect your consideration that I find it meet to back my demand for redress with violence and the threat of more violence? Regardless of how I might make or you might evaluate my case in the abstract, what effect do you consider my actions to have on the legitimacy of my claim?
And, finally: Can you define in rigorous terms why it should be in any way more moral, or less deleterious to the good order and conduct of any society, for many people to engage in actions analogous to those I've just laid out? It's not right or just or meet or permissible for me to act in that fashion, but the common theory seems to be that, if I go out and round up five hundred more who're pissed off just like me and we all come back with shotguns, or Molotovs, or what-have-you, the very same actions are somehow ennobled thereby. I've heard a goodly number of arguments for why that is, but none has managed to convince me; perhaps you'll be the first! In any case, I hope you'll attempt so to do, and look forward to studying the result.