Thomas Sowell's A Conflict of Visions: Ideological Origins of Political Struggles lays out the approach of the constrained vision:
... The constrained vision does not defend existing inequalities, or any given pattern of economic or social results, as just. According to Hayek, "the manner in which the benefits and burdens are apportioned by the market mechanism would in many instances have to be regarded as very unjust if it were the result of a deliberate allocation to particular people." [pg. 139]
This is starting to get to the heart of the matter: the constrained think inequality is unjust only if it is deliberate, while those with the unconstrained vision think it is just to do something deliberate regarding inequality. No wonder they don't agree.