Citizenship & unintended consequences

From Mortimer Chambers's Introduction to The Fall of Rome: Can It Be Explained?

From a different point of view, E. T. Salmon suggests that the action of the Emperor Caracalla, who bestowed Roman citizenship on nearly all free men living within the Empire in 212, actually had an unforeseen and dangerous result. Men who joined the army with the aim of winning Roman citizenship through service were no longer incited to enlist by this presumably strong motivation. Roman citizenship was worth serving for, since it conferred on a man the right to go to court and to make a legal will, not to speak of its social and other advantages. If it could be acquired automatically, this possibility could have discouraged enlistment by noncitizens.