The FN FAL and G3 are the only latter half of 1900s (1950-1999) mainstream small arm systems that I can think of that had the left hand charging handle. Any others? (Stg44 had originally as well.)
The latest generation of rifles with most having hand charging handles, or at least ambi/switchable side charging handles, really seems to only have become a "must have" after the latest Iraq War and all the CQB fighting that American soldiers faced in that conflict. Same can be said for the switch from DI (less reliable) to piston systems (more reliable).
Yes support hand charging handles are great if you're changing mags during the fight and get back into action ASAP, but not really if you're carrying your weapon around all. They're also a detriment to transitions if you have any sling other than single point (and even then there's a good chance of handle to the crotch) and want to throw the weapon behind you to get to your pistol.
Essentially, Iraq in my mind really shaped the operational mindset how our troops fight and the best setup for weapons and tactics. There wasn't a lot of walking there. Most operations were vehicle mounted and most high speed operators spend a few hours in danger zone before being back to the relative safety of controlled access base with little to no likelihood of needing to defend themselves there. Basically, operations there more resembled a law enforcement type of operation where we set the time, place, and number of conflicts and the only time our soldiers didn't was when they were in armored vehicles traveling to the set time and place... I think this can also be seen with the current obsession with SBRs (even M4 carbine length barrels) in 5.56 despite the very real and proven disadvantages of 5.56 bullet performance at lower velocities.
Point being, if you're foot mounted light infantry carrying a massive ruck or at a small forward operating base, always at potential danger, always carrying weapon and in a state of semi-readiness due to constant threat (but not mounted to shoulder as you make a forced entry on your own timeline), not needing to quickly get in and out of vehicles (the primary why behind the switch by Army service-wide to M4s), etc, you have very different weapon requirements and might be willing to make different compromises insofar as what's important to you.
Frankly, there was a lot that tried to be ported from lessons learned and ways of fighting in Iraq by soldiers and leadership into Afghanistan in 2008 that didn't work... Point being, every mission/specific use would have a different definition of optimal. So you try to choose which is best across your most likely scenarios and minimize negative attributes of those "improvements" in the less likely scenarios...
To the point, for high speed type offensive operator weapon configuration (or even for 3 gun and the like), I think the left side charging handles make sense. For a civilian that just wants a rifle to carry around on a sling while working the farm or walking the woods, it probably doesn't.
For me, the deciding factor was to have, as much as possible, the same manual of arms for charging the weapon across all systems. I can't afford to switch/configure all my rifles (and if you're going to be shooting family/friends or even battlefield pickups, conceptually you'd want theirs to be the same as well), so I decided to leave as is as the standardized manual of arms should probably be as quickly as being confused about which side the bolt handle is on under stress. My thought process. YMMV.
