The M-16 was adopted because if was automatic and easy to use. In the days of a draftee force, when DI's had to pretend to make soldiers out of sad sacks like
Gersh Kuntzman, it made sense. The M-14 is a superior infantry weapon, at ranges greater than 100 meters, in the hands of a motivated and well trained troops.
Keep the M-16 for cooks and clerks and the Air Force, but give the war fighters, Marines and Infantry, a real military rifle.