It may be impolite to reject some tribe's word for themselves, but it is dishonourable to assent to a lie, and the latter principle dominates.
As with all American virtue signalling, the American in question holds the vice corresponding to the virtue they espouse. E.g. if they bang on about empathy, it means they are particularly sadistic.
Americans call themselves Progressive when they intend to argue for stone-age sociology.
E.g. when you argue that carbon taxes et al will set the economy back, their true thought is, "Yes? Of course that's the point?" The more paleolithic America becomes, the better. These effects are not some sort of accident or oversight.
In fact I've softballed it. Regressives are trying to reify American myths regarding what stone-age tribes were like. E.g. genuine hunter tribes have very strong laws. You absolutely cannot go against the tribe. Traitors are subjected to heinous deaths - so heinous it's difficult to observe, because it's such a dumb idea that nobody even approaches risking it. It is troublesome to survive even mild disapproval from the village strongman. (Not particularly orderly laws, but strong ones.) By contrast, Regressives like to imagine they had no restrictions at all but could follow their instincts and impulses, like animals.
P.S. See also: Hobbes was basically an idiot.