Defending both left and right against the government is another story, I think. There are more tribes than just left and right, and even left and right I'd see more as meta-tribes, tribes made up of other tribes. Depending on the issue you're looking at, alliances shift, e.g. on Ukraine or Israel where the fault lines are not the typical left/right divisions in most Western countries.

That "law" probably resonates with lots of people who aren't fans of conservatives, but that's a low bar to clear and doesn't say much about whether it's true and only conservatives form tribes (calling everything conservative that forms a tribe would turn it into tautological reasoning). Every political movement I've ever witnessed was tribal at its core. I'm not sure it's impossible to have a cohesive movement without forming a tribe, but it doesn't seem to be easy or we'd see it more often.