Kin altruism does not make much sense outside the nuclear family, or narrowly extended family. It can work in slightly larger groups if they deliberately practice inbreeding, but the groups are not much larger, and you get IQ depression from inbreeding.

So what explains the tendency of ethnics to stick together?

Well if people resemble you, they are predictable. You know you can trust them in some matters to some degree. So you do. This makes reciprocal altruism workable. Mix in outsiders, and you lose trust. Thus Jews thought they could trust Madoff to cheat gentiles, and not cheat his fellow Jews. Because Jewish cohesion has been diminishing for some time, this turned out to be a bad expectation.

Another thing that causes loss of trust is mandatory lying and betrayal. Hence when east Germany and west Germany were reunited, the east Germans appeared to the west Germans to be subhuman, even though there was no significant genetic difference. East Germans would not work unless someone was standing over them, and would cheat, lie, and steal for any momentary slight advantage. The difference seems to have diminished now that they have been living under the same political system for a while.

People are not going to be altruistic to whites just because they themselves are whites, and Jews are not altruistic to Jews just because they themselves are Jews. This is a Nazi fallacy. Comradeship of whites is no more workable than comradeship of the proletariat. Whites have always been primarily at war with whites. This is not caused by sneaky Jewish mind control rays. Man is wolf to man, and whites are wolf to whites.

Good behavior is trustworthy and honorable behavior, not benevolent behavior. People who claim to be benevolent to far away strangers seldom are, and when they are, their benevolence is disturbingly and dangerously selective and capricious. This is yet another reason why utilitarian theories of morality don’t work. Not only is no one utilitarian, no one is benevolent.

Altruism is unworkable for any group above a dozen or so people. Trust is scalable to vastly larger groups.