Naturalism is the philosophical theory that treats science as our most reliable source of knowledge and scientific method as the most effective route to knowledge.
That doesn’t mean anyone should stop doing literary criticism any more than forgoing fiction. Naturalism treats both as fun, but neither as knowledge.
What naturalists really fear is not becoming dogmatic or giving up the scientific spirit. It’s the threat that the science will end up showing that much of what we cherish as meaningful in human life is illusory.