Another aspect of right side charging handles completely missed in this discussion is that they are much more easily manipulated and opened when standing in ranks for inspection. The Old School Army had much more drill and ceremony in the daily schedule, open ranks inspection was frequent, and with weapons inspection, much more easily done with a right side charging handle.
From side lock muzzle loader, to bolt action, to gas action, multiple generations of soldiers were taught and passed down the rituals of Inspection Arms, and considered it to be important that the weapon conform to easy manipulation. Tactical requirements in the field have always been slow to adopt and hard to document and justify.
What is now appreciated is that a left hand charging receiver can be cycled by the off hand while the weapon is held up and aimed. Much of the reason is that it's not an 11 pound .30 caliber - try holding any 50's battle rifle by the right hand and shoulder only. It's not really feasible - but with the light assault rifle pattern with pistol grip, much more so. A rapid bolt cycle is not only possible with the sights on target, present tactics use it more often because the soldier is upright and moving over ground wearing armor, not prone, covered, and protected enough to take the time.
What you are seeing is 1930's battle tactics vs. 2010. Look at the modern carbines introduced for sale, adopted for use, and track the overwhelming trend for a left hand charger upper. With some design elegance, they even swap sides and allow lefties the same ability, trigger hand on the grip and off hand cycling the bolt.
Why even bother? Because more shooters DON'T use the handle as a forward assist. The reaction response to a jam is jack that round out and even replace the magazine. You can do that faster, and the likelihood of returning to 100% effectiveness is much higher. Figure out what's wrong with it later, there are shooters aiming at you. Pushing a bolt forward on a reluctant round is much more likely to make things worse than better.
Modern designs have off side charging handles and controls that help the shooter stay in the fight, shooting, with frequent mag changes and a lot of rounds going out. Tactics have changed, weapons are changing with them.
