I've never been real fond of the sheepdog metaphor.
I go about armed, but do not see myself as a protector of others. Would I step in and help another? Sure, but only if circumstances are clear.*
I think the author is adding an unnecessary significance. I don't need to think of myself as special, or a sheepdog, or a self-appointed protector. My self-esteem and identity don't need it.
But, hey, if the author or a reader needs a little boost for his self-importance, OK by me.
For myself, folks will find Ben Franklin's comment on democracy a little more accurate. Franklin said (paraphrase), "Democracy is two wolves and a lamb voting on what to eat for dinner. Liberty is a well-armed lamb contesting the vote." Think of me as an armed lamb.
*Unfortunately, the genuine sheepdogs (police) seem to tolerate wolves in their midst (Blue Wall of Silence). Helping others in a lethal force or threat of lethal force situation can be a little dicey and not just from the perspective of getting hurt yourself. Witnesses have been known to turn and support the wolf during the after-shooting investigation. Also, the genuine sheepdogs seem to be sometimes unable to distinguish armed citizens from wolves, the poor armed sheep then having to defend himself in court.