The Piketty/Saez logic is typical of the French Left which believes in a Lump of Wealth theory akin to its belief in the Lump of Labour. In other words, there is a fixed amount of wealth in the economy each year regardless of cause and effect or creative dynamism on the part of independent economic actors; if some get more of this wealth than others, it’s because the polito-economic system is unjust. Ergo, redistribution can create ‘social justice’ and need have no adverse effect on the aggregate of national wealth because that is always there, somehow (delivered in a bag to the Treasury every Jan 1 by fairies, for example). Adherence to the Lump of Labour theory is what gave rise to the economically disastrous 35-hour week inflicted on France by Leftist politicians who believe that political will is sufficient in itself to dictate desired economic outcomes regardless of actual, existing realities. Economics is despised by Parisian political theorists as a vulgar, money and commerce tainted Anglo-Saxon affair which compares badly with the morally-uplifted French pursuit of social compassion. Which may be why Piketty and Saez don’t care to notice that if the dynamic rich didn’t exert themselves to create all that wealth, it would never exist to be redistributed.