Just read this fantastic post on Piketty’s book by Eric Falkenstein. He tears apart Piketty’s nonsensical work (the guy seriously believes it is a law of nature that the return on capital (r) is bigger than the growth rate (g) in the economy over the long run) step by step. Falkenstein’s arguments touch a variety of topics and show that he possesses tremendous interdisciplinary knowledge.
Read it. Memorize (and understand) his arguments and confront your egalitarian friends with them!