You exposed the contradiction in liberalism as a political philosophy very nicely. Maybe a look at the origins of liberalism as a political philosophy would help bring more light to the issue. Wasn't it a vehicle to further the interests of the merchant class in their battle to wrest power from the aristocracy? And as an expression of human aspirations, it may have been an early attempt to express a dawning awareness that all people deserve the same rights, a universal outlook. Here is another level of the contradiction between the ideal and people's baser tendencies.