Beginning with Leo XIII, a growing body of “social doctrine” was developed in keeping with world events in those fields, always faithful to the values of freedom, truth, justice, love, and peace. This explains why from Rerum Novarum onward the Church’s opposition to utopian socialism has always been at the fore, aiming at the core of socialism as being contrary to human nature and Judeo-Christian revelation. At the same time, the Church’s criticism of liberal capitalism has been directed not to the system of free enterprise, free markets, and private property as such but to the injustices and immoralities spawned by an unprincipled liberalism that can easily creep into such a system unless it is imbued with objective ethical and religious values, which alone can make liberty and democracy workable.
Joseph M. de Torre, "The Pontificate of Leo XIII (1878-1903) and the Encyclical Rerum Novarum," Journal of Markets & Morality 14, no. 2 (Fall 2011): 319-325