I can understand during the era there was a need to use the M14 in full auto. However, in the current times the use of burst or auto on a rifle is just stupid.
I was in the Infantry (0311) in the Marines. At no time is there a reason to use a rifle (M16A4/M4A1) in anything but semi-auto. To do so is a complete waste of ammunition, you only carry so much with you on a patrol. That is what your Automatic Rifleman is for. If that was your role (which it was for me) in the fire team, you carried a M249 SAW (Squad Automatic Weapon) and provided the automatic fire for your fire team.
As I told someone earlier, I was an artillery scout observer with a grunt company - so I carried what I could get away with. Most of the time I was busy with fire missions but once we took some casualties and the Medevacs started, I became an ad hoc automatic rifleman. The grunts appreciated me because I was good.
About five years after I came home, I was recognized by one of the Golf Company Marines while I was attending Cal State Northridge and he told me that they "really missed me and my M14" after I got hit and sent home.
Well-aimed and properly employed automatic fire is essential sometimes and if your Marines are well-trained it won't be a waste of ammo.
The Marines have introduced the M27 IAR (basically a modified HK 416) to supplement the SAW with more automatic riflemen. The latest word is that the Marines are considering replacing *all* their M16s and M4s with M27 variants.
http://www.military.com/daily-news/2016/11/18/marine-corps-experimenting-new-service-rifle.html
http://www.thetruthaboutguns.com/2017/02/foghorn/marine-corps-may-replace-fns-m4-hks-m27-iar/
If so, good riddance to direct impingement burstfire guns.