This paper argues that public reason cannot form a fair basis for determining whether religious exemptions to laws of general application are justified. This is because the fallibilist moral psychology required to ground the plausibility of public reason as a justificatory mechanism is not shared by committed religious believers. This difference is even more pronounced in the case of religious institutions, who typically do not take a fallibilist approach their central doctrines. As a result, I claim that liberal theorists invested in the idea of public reason must either declare all such committed religious believers unreasonable or otherwise abandon liberal neutrality with respect to religious conceptions of the good. Finally, I show that this argument has significant implications for the way in which courts use proportionality analysis as a way of adjudicating disputes involving religious liberty claims and anti-discrimination law.