Answer:
With this statement, McElvaine meant that social justice is the only way to promote the same privileges to all members of a society and that is what a common good must do.
Step-by-step explanation:
Commonly, it is the term that refers to benefits that are distributed equally to all members of society, so that they all have access to exactly all the resources necessary for their well-being. When McElvaine claims that common good is best achieved by promoting social justice over economic liberty, she/he meant that only social justice, that is, the view that all individuals deserve the same rights, opportunities and privileges, is capable to promote this equal distribution of social resources. For this reason, social justice must be sought first, so that economic freedom can be achieved later.