RE: I want people to be able to buy Gold Dust if they want to
I guess I'd have to say I MOSTLY agree with you. I think the level of possible harm/damage matters. If someone is selling snakeoil and the worst thing that could happen is some people spend money and are disappointed with results, whatevs. As you mentioned, they might get some peace of mind, or a placebo effect, or some other thing that I don't care about because I too want people to be able to do whatever they want(for the most part) But if say the worst case, and maybe the likely case is death or debilitation, then no it's not worth the lives that it would ruin before enough people die from something to get the word out and have people stop buying something because it's killing them. If it could be proven that something has a very high likelihood of extreme harm, I wouldn't want that person or entity allowed to sell that product.
Things like alcohol?
The effect of alcohol or say cigarettes is cumulative. You won't die from smoking one or two cigarettes or taking a couple shots of vodka. In my mind this should be reserved for if someone is literally selling deadly poison, that is not labelled as deadly poison, not just something that's bad for you. I'd even go as far as saying I'd support people being able to buy suicide pills or something along those lines as long as they knew what it was. But not, "Miracle pill" that actually just paralyzes you or kills you or gives you debilitating brain damage.