Thanks, Joseph. You got my vote, of course. On that basis, allow me to offer some perspectives, not in disagreement but as alternate viewpoints.
Foremost, the affection for the supposed underdog is a consequence of Christianity. Make no mistake; make no compromise. The meek shall inherit the Earth. Nietzsche flogged this horse. Ayn Rand was attracted to his context, but realized that in specifics, he was greatly lacking. Nonetheless, the fact remains that Christianity is the common theme that unites supposedly secular socialists with their kith and kin on the religious right.
It was not always so. I do not remember the specifics of name and place, but in Thucidides's history of the Peloppensian Wars, is the story of Athens against a small island city. In the wake of Athens's victory over the Persians, she established a hegemony. Other cities paid tribute to her. Eventually, one of them balked at forking over the silver. Athens sent an army. In Thucidides you will find the story. The city fathers call upon justice and natural rights. The Athenian general replies that it is just and naturally right that the strong should rule the weak, and that their cries are like the cries of the rabbit in the talons of the eagle.
Objectivism is beyond "might makes right" but is clearly not aligned with "lack of might makes right."
Secondarily, those who are touted as underdogs, often are not. The Nazi Germans portrayed themselves as victims as their justification for launching aggressions against their neighbors. Moreover, often, those aggressors - the Nazis, the communists, ISIS now - often sell themselves as the wave of the future. They claim strength. Admittedly, it is a strength that they lack, but, nonetheless, they do not portray themselves as weak and helpless.
As you note, though, others prefer to see them that way. That ties in to the Christian ethos, which is common across even secular socialist bands in the modern political spectrum.
But is it not limited to the Left. In a criminology class, the textbook and discussion were all about justifying rap music as a consequence of oppression. I pointed to heavy metal and white supremicism as a counter-example. "You think that it is hard getting a job when you are Black, try getting one with a swastika tattoo on your hand." I condemn them both. They are both racists. But they both claim to be underdogs, oppressed minorities. They do not say - as did the Communists, and as does ISIS - "we will bury you."
Your deeper - and I admit, perhaps intractable - challenge is "When is a threat a threat?" I do not know. Like you I know one when I see one, but I do not have a universal rule that subsumes all possible examples. I have no conceptual solution. Like you, I can only take specific cases: This one feels like a threat; that one does not.
(Edited by Michael E. Marotta on 7/01, 4:02pm)