Discussions in contemporary epistemology are burdened with confusions about the terms “rational”, “rationality” and their antonyms. In economy, for an agent to be rational simply means to satisfy the Bayesian probability axioms, but the situation in philosophy is much more complicated. Two kinds of rationality are usually distinguished. Epistemic rationality is an ability to achieve justified and true beliefs, whereas instrumental rationality is a capacity to act in accordance with one’s own interests. This division cleared the way to contemplation about rational irrationality, which is the case when an acceptance of epistemically unwarranted beliefs may increase instrumental profit for an individual. In my article, I will criticize this approach. The proponents of rational irrationality 1) misunderstand the primacy of epistemic rationality over instrumental one; 2) underestimate social nature of normative terms; and 3) misinterpret the evolution of human cognition. I will illustrate my conclusions with an example from applied epistemology – conspiracy theories. It is misleading and disparaging to use the term “rational” in relation to sets of unjustified beliefs that are based on conspiratorial ideation. If philosophers cannot make their ideas on rationality clear, it might be better to leave out rationality completely from the epistemological discourse.