If Sam and I are engaged in some activity A, and Pat comes along and punishes Sam for A or otherwise interferes with Sam's ability to engage in A...
...if on reflection I endorse A, then I endorse interfering with Pat and aiding Sam, for several reasons: it results in more A, it keeps me from feeling like a coward and a hypocrite, and I establish myself as a reliable ally. I consider that one of the obligations of social alliance.
...if on reflection I reject A, then I endorse discussing the matter with Sam in private. Ideally we come to agreement on the matter, and either it changes to case 1, or I step up alongside Sam and we take the resulting social status hit of acknowledging our error together. This, too, I consider one of the obligations of social alliance.
...if on reflection I reject A and I can't come to agreement with Sam, I endorse acknowledging that I've unilaterally dissolved the aspect of our social alliance that was mediated by A. (Also, I take that status hit all by myself, but that's beside the point here.)

I agree with you that if I instead skip the reflective step and reflexively endorse A, that quickly degenerates into pure tribal warfare. But the failure in this case is not in respecting the alliance, it's failing to reflect on whether I endorse A. If I do neither, then the community doesn't degenerate into tribal warfare, it degenerates into chaos.

Admittedly, chaos can be more fun, but I don't really endorse it.

All of that said, I do recognize that explicitly talking about "social alliances" (and, indeed, explicitly talking about social status at all) is a somewhat distracting thing to do, and doesn't help me make myself understood especially well to most audiences. It was kind of a self-indulgent comment, in retrospect, although an accurate one (IMO).

(I feel vaguely like Will_Newsome, now. I wonder if that's a good thing.)