Poststructuralism was created as an attempt by a certain group of Marxists who had given up on the usual ways to try to win people over to their political philosophy, and decided instead to persuade them there is no reality (or at least no way to know it, which for practical purposes amounts to largely the same thing,)and therefore all the standard arguments for liberalism are false, and we are free to create Marx's utopia. See for instance Hardt and Negri on all this. As a political strategy it has simply failed, though it has helped cause to a lot of the political problems we face today.