There is never a right reason for a generalization. Voicing such things are the true causes of conflict, not any particular random or group.
If two gays are rubbing their orientation in your face, then by your standards that automatically means all gays are in the same pod.
Did you know a majority of the national socialist armies in WWII didn't even know of the atrocities being committed against Jews? Those who killed the Allies or pro-semites simply did so because they were ordered to.
To say all national socialists were evil is a generalization.
Generalizing is what causes conflict, Ike. Not the groups themselves.
Unless you're talking about al Queda, there is no reason for a generalization.