Expanding on a couple centuries of economic thought that equates "rationality" with self-interested action, current research points out that acting in our self interest may also entail acting against inequality. Just maybe, at least under certain circumstances, we really do want to share the wealth.
Scientific American explains.
[In a recent study, Swiss Neuroscientist Ernst] Fehr and colleagues show that, in a sample of 229 children between theages of three and eight years, younger subjects overwhelmingly conform
to selfish (self-regarding) preferences. They don’t like to share and
aren’t interest in reducing inequality. In contrast, the vast majority
of the older subjects are inequality averse when put in either the
advantageous (individual A) or inadvantageous (individual B) position.
Moreover, the researchers find that the older children are “rational” in the sense that they are more willing to share when the cost of doing so is low than when the cost is high. Finally, the children tend to be more inequality averse in dealing with 'ingroup' members, or children from their own school or day care. This preference for sharing with ingroup members occurred even the sharing game was purely anonymous, so no child could determine the identity of the other players.