You said prohibition never works, I just gave you a list of tonnes of banned compounds that there is no underground market for. Sometimes, banning things works. Unless there's a huge demand for something that has incredibly potent effects, and is relatively easy to produce. If smoking was banned, some people would be upset but you wouldn't see a huge demand for cigarettes like we do cocaine, marijuana, all of the opiates, etc. etc.
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Your everyday smoker isn't smoking to get high, if they banned smoking, most smokers would suck it up, and in a few months realise "holy shit, my lungs feel way better!"