This the point where your typical lefty friend is stumped. And then your righty friend jumps in and says: aha, yes this shows that most importantly we want total wealth to increase. A rising tide lifts all boats etc. And then your lefty friend says: well if it wasn't for evil capitalists then the Ethiopians wouldn't be poor in the first place! To which, righty says: No, not evil, wealth creator! And lefty: No, what about the monopoly abuse... And so on. Until they both sink in intellectual quicksand. When they finally stop, instead of answering the real question we started with, lefty goes back to his original assumption that inequality is the root of all problems and right goes on thinking all rich people deserve it.
Here's a simple test to make this more productive. Always ask first: When you are talking about inequality are you really talking about injustice? Almost every case where someone speaks of a concrete example of inequality, when you peal through layers, they really mean material injustice. They are against the *way* wealth is obtained. Whether it is Wall Street or kleptocrats in poor countries, the real root of the accusations is theft, abuse of power, denial of opportunity, corruption, and especially regulatory capture. And those are usually clearer issues with clearer solutions.
Of course clearer doesn't mean easier. Justice is hard by itself. But if you seek real understanding, in each instance, first look at injustice. When you have fully considered that, often you will find the issue is fundamentally injustice. The rest, as they say in research, is implementation details.
Now in the rare cases where there really is no injustice, there is something to say about inequality. When you rigourously examine what people can actually defend, it is not the overall inequality. Say one independent worker is at the 40th percentile because they want time for their hobbies; and another person works twice as much and ends up at the 80th percentile. Few people would argue that the second person should subsidize the first. When you get down to it, morally the case is: help those at the bottom. Yet, when politicians talk about inequality (in the US especially), it's always about the middle. Middle class this, middle class that. How come?
Because the real issues they are talking about are actually issues of injustice. And if you are part of the machinery of said injustices, then the best way to avoid dealing with questions of injustice is to roll them into with the incoherent debate about "inequality". That will make sure everyone is so confused they will think you are the good guy. That is also partly why both the Tea Party and Occupy Wall Street movements became what they are. They both started out as rebellions against bail-outs. Now they are mainly fighting against each other while being directed by their former targets. Political jujitsu.
So if you, dear reader, are a kleptocrat, congrats! It's working. If you are not, then please don't get confused. Focus on injustice.
P.S. The jujitsu works because of fundamental human traits: desire and scapegoating. I recently came across the thoughts Rene Girard. That deserves its own post.