Liberalism is inherently incoherent and anti-human. The more liberals attempt to be fully self-consistent, the more incoherent and anti-human their demands become: thus the anarchist tyrant as the liberal pseudo-telos.
But liberalism has an additional feature, the unprincipled exception (a concept explored in some depth at Lawrence Auster's blog View from the Right), which prevents it from immediately self-destructing.
Illiberal principles are not permitted to assert explicit authority in the liberal order. But because liberalism is incoherent and ultimately self-destructive, something has to keep things from falling apart: something has to assert a stabilizing authority in order to hold things together. This thing, this assertion of illiberal authority which is not permitted to be explicit but which nevertheless has effect, is the unprincipled exception. Unprincipled exceptions are often asserted as an appeal to common sense, an assertion that to take things to the rational next step clearly demanded by liberal principles is "silly", etc. But unprincipled exceptions are never permitted to explicitly challenge liberalism itself. They exist to dampen the advance of liberalism enough to keep it from self-destructing. As a form of parasite liberalism is incapable of existing on its own, and unprincipled exceptions, originally vestiges of the moral core of Christendom rendered mute but still in effect through appeals to common sense or some other euphemism tantamount to "shut up", have been what has kept liberalism - ultimately an authoritative assertion of the illegitimacy of authority, which is the same as asserting the free and equal superman - in power.
Now, liberalism is not a formal Platonic system which exists "out there" all at once as a fully fleshed-out self-consistent Form or whatever: it is a (ultimately incoherent) political ideology which exists in time, and which is adhered to at any given time, by more or less loyal liberals in a more or less consistent manner, in an historical context. In its relentless pursuit of political emancipation from history, tradition, nature, and nature's God, liberalism eats up and destroys traditional authorities, including eventually the very unprincipled exceptions which have sustained it at any particular point in time. But liberalism's vision of reality, of what is possible, is false. So where yesterday's unprincipled exceptions were vestiges of traditional authority (think prohibition or at least shunning of divorce), today's unprincipled exceptions are new ones invented by liberals themselves (think prohibition or at least shunning of pollution - a comparison I've drawn before to much wailing and gnashing of teeth). Because they are new, and invented by liberals, they carry less of the whiff of the untermensch - the traditional oppressor of the proto-superman - and are therefore more tolerated by liberals.