From Slavoj Žižek: Towards a Materialist Theory of Subjectivity :
“You know why I think he is utopian? He is in a way right. The twentieth century overcoming of capitalism didn’t work, but he then generalizes this implicitly, he accepts, as a good Keynesian, that capitalism is ultimately the only game in town; all alternatives ended up in fiasco, so we have to keep it. He is almost a kind of a social-democratic Peter Mandelson, you know the dark prince of Blair who said that in [the economy] we are all Thatcherites. All we can do is at the level of distribution; a little bit more for health care, education and blabla. So what I’m saying is that I think he’s utopian because he simply says that the mode of production has to remain the same; let’s just change the distribution by, nothing very original, radically higher taxes.
Now here problems begin, here the utopia enters. I’m not saying we shouldn’t do this, I’m just saying that to do this and nothing else is not possible. That’s his utopia. That basically we can have today’s capitalism, which basically as a machinery remains the same just oh oh oh when you earn your billions oh oh here am I tax, give me 80 percent. I don’t think this is feasible. I think, imagine a government doing this, Piketty is aware it needs to be done globally. Because if you do it in 1 country, then capital moves elsewhere blabla. This is another aspect of his utopianism, my claim is that if you imagine a world organization where the measure proposed by Piketty can effectively be enacted, then the problems are already solved. Then already you have a total political reorganization, you have a global power which effectively can control capital, we already won.
So I think in this sense he cheats, the true problem is to create the conditions for his apparently modest measure to be actualized. And this is why, again, I’m not against him, wonderful, let’s tax them 80 percent. What I’m claiming is that if you were to do this you would very soon discover that this would lead to further changes and so on and so on. I’m saying that it is a true utopia, and this is what Hegel meant by abstract thinking, to just imagine you can take one measure and nothing else changes. Of course it would be wonderful to have today’s capitalism with all its dynamics, just at the level of redistribution you change it, but this is utopian. You can not do it, because a change in redistribution would effect the mode of production, capitalist economy itself, I don’t know in what way. I’m just saying that sometimes utopia is not anti-pragmatic, sometimes to be modest in a false way is the greatest utopia.”