I'm not familiar with those claims of Zizek's, but they sound like defenses of postmodern superficiality and play. The Achilles heel of that stance is science. Scientific knowledge isn't just of appearances in any ordinary sense. Science may not be noumenal in the Kantian sense, but scientists show us how nature objectively works, not just how nature appears to us as individuals. At most, we could say with Kant that science is about how nature appears to intelligent beings in general. But science also tells us about how the universe will be long after there's any life in it.
Our investigative tools impact the content of experience mainly in quantum mechanics. But I take up some other postmodern themes when I talk about the Promethean, Luciferian aspect of science, such as here:
