> X increasing is an indicator that Y is increasing. Therefore we need to increase X more in order to make Y decrease.
The issue is that inequality is growing to a point that there is a potential for social, economic, and political destabilization. How do you propose the issue be addressed? Because it should be apparent that trickle-down economics isn't occuring, and I don't see how things can improve without some sort of wealth redistribution.
I would actually recharacterize Piketty's (and the author of this chart) argument as:
"X increasing is a symptom that Y is increasing. Let's implement policy A. This may temporarily increase X, but it will stop Y from increasing, which will in turn stop X from increasing in the long run."