[cc439]

The problem with bare 18650 cells is in their chemistry. A bad charger + good cell = nasty fire and a good charger + bad cell = the same. Considering the fact that every major online retailer including Amazon has trouble policing fake cells, the liability risks are fairly extreme. If there was a way to completely block all non-UL rated products as well as those with fake UL stickers, I'd say your idea has merit. Unfortunately, the near frictionless world of online markets allows for too much counterfeit risk to enter the picture for such an idea to be workable.