Conservatives are happier than liberals, the story says, because "conservatives rationalize social and economic inequalities" with their "tendency to justify, or explain away, inequalities".
Which is a just a backward way of saying that because liberals can't get used to reality they engage in a lifelong temper tantrum punctuated with periods of pouting.
It makes 'em sad. Poor blighters.
Children know life is not always fair. Liberals, apparently, are not so well-adjusted.