It's not circular logic. Zizek is operating from the assumption that capitalism is oppressive, and arguing that "socially responsible" capitalism is equally as problematic. This criticism is aimed at leftists who dislike capitalism, but feel like it's okay to engage in "socially responsible" capitalism. It's completely legitimate to disagree with that assumption, just keep in mind that is not the point he's trying to argue in this video.

He's also an unapologetic Marxist, so I suppose that'd be his alternative. You might start looking for answers to your questions in his books.