I watched a drug addict lovingly turn a plain lightbulb into a meth pipe.

Sure, and aluminum foil can be used to smoke heroin. But they have primary obvious uses. That's the difference, vs knowing 99% of customers are going to use it for something nefarious. Even better example would be whippets or NOs meant for culinary or automotive use, but also usable for teens getting high. If manufacturers are aware and turn a blind eye, they can become liable.