Rerum Novarum was written long ago, when Marxism and a socialist society were thought of progressive.  The message of Rerun Novarum was largely superceded by the wisdom of Centesumus Annus, recognizing how 100 years (hence the name) of socialism led to horrifying disasters of the 20th century.  If your reading of Church teaching stopped at the hoary old Rerun Novarum, it's YOU who needs further education.