If Socialism, like all errors, contains some truth (which, moreover, the Supreme Pontiffs have never denied), it is based nevertheless on a theory of human society peculiar to itself and irreconcilable with true Christianity. Religious socialism, Christian socialism, are contradictory terms; no one can be at the same time a good Catholic and a true socialist.
Pope Pius XIMan cannot be exempted from his divinely-imposed obligations toward civil society, and the representatives of authority have the right to coerce him when he refuses without reason to do his duty. Society, on the other hand, cannot defraud man of his God-granted right... Nor can society systematically void these rights by making their use impossible.
Pope Pius XIWhen once men recognize, both in private and in public life, that Christ is King, society will at last receive the great blessings of real liberty, well-ordered discipline, peace and harmony.
Pope Pius XINo vicarious charity can substitute for justice which is due as an obligation and is wrongfully denied.
Pope Pius XIEducation belongs pre-eminently to the church ... neutral or lay schools from which religion is excluded are contrary to the fundamental principles of education.
Pope Pius XIIt violates right order whenever capital so employs the working or wage-earning classes as to divert business and economic activity entirely to its own arbitrary will and advantage, without any regard to the human dignity of the workers, the social character of economic life, social justice, and the common good.
Pope Pius XI