The warning is there so that if people can't be bothered or are simply too stupid to comprehend the directions eat the things, the manufacturer can't be held liable because some whiny charlatan of an ambulance chaser talks the next of kin into a law suit.

Used properly by someone who is at least a simple idiot (rather than a special idiot) they are perfectly safe if you can stand the smell, and even if they don't save your life directly they at least remove one potential problem. Used improperly, Darwin in action. Just like toothpaste, deodorant, pens, a cup of coffee, a coffee cup, cleaning products, elevators, gasoline, lighters, knives, firearms, power tools, electric lights, automobiles, water, food and oxygen.