In fact, their role is to serve as Viagra to the State. This becomes apparent when one considers their position on the increasingly virulent question of migration. Left-libertarians are typically ardent advocates in particular of a policy of 'free and non-discriminatory' immigration. If they criticize the State's immigration policy, it is not for the fact that its entry restrictions are the wrong restrictions, i.e., that they do not serve to protect the property rights of domestic citizens, but for the fact that it imposes any restrictions on immigration at all.
But on what grounds should there be a right to un-restricted, "free" immigration? No one has a right to move to a place already occupied by someone else, unless he has been invited by the present occupant. And if all places are already occupied, all migration is migration by invitation only. A right to "free" immigration exists only for virgin country, for the open frontier.