The difference is based on how people perceive the inequality. If it is seen as being unfairly earned, it severely hurts the incentive to work (through, say, p

The difference is based on how people perceive the inequality. If it is seen as being unfairly earned, it severely hurts the incentive to work (through, say, paying lower taxes than poorer people, being awarded business through lobbying or social classes, being born into wealth, exploiting or underpaying the working class, or more generally anything where random Person On The Street couldn't do the same thing). It doesn't matter what the outcome is, as long as it is seen to be fair. As soon as it isn't, people will resent the system, subvert it or rebel. This is a trait we share with monkeys and elephants, and is possibly the basis of social organization.