right, I understand that point. My dad is a former marine from back in the 60s during the brief M-14 lifetime and told me that it used to be that only ONE man in the entire squad would have a fully automatic weapon (in WW2 it was the BAR and just about everyone else had the M-1) when he was in only one of the men in a squad would have an capable of M-14 shooting fully automatic. They didn't want every man just spraying and praying. The idea was primarily suppression fire for assult and to fortify for defense.
While you are right that it is better on once since to make one shot count on each opponent with a revolver or semiauto pistol or rifle, there is rhyme and reason behind a fully automatic weapon.