Is democratic Keynesianism possible?

Chris Dillow asks Is democratic Keynesianism possible?.

In this sense, I read Simon as making a very radical claim — one which is more Marxian than Keynesian. "Democratic" policy-making cannot serve the public interest, because it is subverted by capitalists' interests. This represents a challenge to naive social democracy, which thinks that governments can do the right thing if only they have the will and courage.

Emphasis Mine

Dillow is correct in saying that the state exists to serve the interests of the ruling class. Under Capitalism, the ruling class consists of Capitalists. Thus, the Capitalist state serves and protects the interests of the Capitalists.