I like the part where it is supposed that rcr123 batteries are the only rechargeable cells in existence.
While it is true that the rcr123 (or 16340 in standard lithium-ion nomenclature) are such a niche battery as to only be manufactured in China, and are inconsistent in both external dimensions and internal capacity from even reputed names, the majority of 16650 and 18650 cells are made by global brands in Japan such as Sanyo, Samsung, and Panasonic, and are just as reliable as disposable lithium batteries when used properly. If you are competent to maintain an AR-15 you are competent to properly employ rechargeable lithium-ion batteries.
Granted, lithium-ion batteries will self discharge over time. They will also become damaged if they are depleted past their minimum voltage. The former makes them perhaps not as suitable for self-defense firearms, the latter can be addressed with a circuit board, on the battery or in the flashlight driver, that cuts power past that voltage, or at least offers a warning in the form of flashes and a reduced output.
These are points that should also be addressed when bringing-up this topic.