Sloppy Liberal Thinking About Equality

Equality of opportunity is one thing, equality of outcome quite another.  The former is a necessary, but not a sufficient, condition of the latter.  Yet many liberals think that any lack of equality of outcome for a given group argues an antecedent lack of equality of opportunity for that group.  This is a non sequitur of the following form:

P is necessary for Q

Ergo

~Q is sufficient for ~P.

This is an invalid argument form since it is easy to find substitutions for ‘P’ and ‘Q’ that make the premise true and the conclusion false.  For example, being a citizen is necessary to be eligible to vote; ergo, not being eligible to vote is sufficient to show that one is not a citizen.  The conclusion is false, since there might be some other factor that disqualifies one from voting such as being a felon, or being under age.  Similarly, an unequal outcome is not sufficient to show discrimination or unequal opportunity for the simple reason that there might be some other factor that explains the unequal outcome, such as a lack of competitiveness, an inability to defer gratification, or a lack of ability.