Mater et Magistra §117

¹¹⁷ State and public ownership of property is very much on the increase today. This is explained by the exigencies of the common good, which demand that public authority broaden its sphere of activity. But here, too, the "principle of subsidiary function" must be observed. The State and other agencies of public law must not extend their ownership beyond what is clearly required by considerations of the common good properly understood, and even then there must be safeguards. Otherwise private ownership could be reduced beyond measure, or, even worse, completely destroyed.