I served in the US Army and am a left handed shooter. One can shoot a typical AR15, AR10 or M4 either way; the main issues are using the bolt release and brass ejection. But both are not a major thing at all. A little scalding hot brass down the shirt merely serves as a wake-up call ;) In Civilian life, it’s still not needed to get a true leftie rifle, you can get an ‘ambi’ version and there’s several excellent manufacturers. But, the guy’s point remains. The ROI makes no sense in one case and even less in the other.