Two of my always well-thought commenters, Jehu + RightSaidFred, suggest that low-ingroup focus in ethics leads to extinction. I'd like to nuance that position a bit.
The Aretae position is that which ethic is appropriate is fundamentally a question of what kind of world we live in.
Jane Jacobs suggested that folks whose job it is to protect (Military, Police, Firefighters, perhaps doctors) need one ethic, while folks whose job it is to trade stuff (Merchants, business folks) need another ethic.
Much later, Robin Hanson proposed an analagous ethical pairing: Forager/Farmer. Fundamentally, folks who are rich need a different ethic than folks who are poor. This is observable by noting that in fact folks who are rich (Rich Americans now, comparatively rich hunter/gatherers of 20,000 years ago) have very different ethics from folks who are poor (normal Americans 75 years ago, Egyptian peasants 5,000 years ago).
I will argue that it comes down to a relatively small distinction: Do we live in a world of high scarcity, and low possibility, or the opposite.
If we live in a world where survival is questionable, and where the primary questions in survival are distributive justice, because we're already awful close to our Malthusian limits....in that case, to not follow a high ingroup-morality is group-destructive.
If, on the other hand, we live in a world far removed from the malthusian limits, and the questions in life are about flourishing or wealth-creation, then a high-ingroup morality is nuts...in that case, the quality of life one experiences is significantly to substantially a question of how effectively one trades. Wealth (the mega-metric) is fundamentally a question of trading. The tighter your ingroup ethic...the less you get along with the fact that comparative advantage (interacting with folks who are unlike you, and the more unlike, the better ) is the basis of economic growth.
In different words...I am with Virginia Postrel...the fundamental dispute is not liberal-conservative....it's wealth-creation dynamism vs. wealth-maintenance stasism.