Larry Alexander argues that liberalism is internally incoherent, because it contains a paradox: it is committed to toleration, but if it tolerates illiberal ideas and practices, it betrays itself.
The paradox does not exist. Liberalism aims to tolerate as much diversity as it can consistent with the preservation of the liberal project. It has distinctive reasons to tolerate illiberal ideas, since it aims to be adopted by the citizenry consciously and with a full understanding of the alternatives. How much diversity can in practice be tolerated is a contingent question dependent on the facts of any particular time and place. Whether domestic fascists, for example, need to be suppressed in order to avoid disaster, is a matter of prediction based on local knowledge. It is not a philosophical question.
I elaborate the point in a forthcoming article in the San Diego Law Review, available here.