It's extremely important if you're interested in social stability. Unhappy people have a tendency to turn authoritarian and lash about, hurting both their own society and anyone who looks different.
I dunno, "discontent" is a pretty politically charged word, going back to Shakespeare - "Now is the winter of our discontent" from Richard III is referring to an attempted political overthrow.
Unhappiness sounds much more pedestrian.
Authoritarianism is usually imposed from above, not below.