> IMO, the optimal attitude for society would be if everyone was "left-wing" (generous, forgiving,...) toward others/out-groups and "right-wing" (demanding, requesting responsibility,...) toward yourself/in-group.

That's rather odd, because if anything I'd say the opposite is best - you can trust your ingroup to have similar values to you, and thus can afford to forgive them/be generous without being taken advantage of. On the other hand, outgroups WON'T share your values, and being more generous to them than to the ingroup is just self destructive.

And I would have thought both of those were common sense, too.