Selling snake oil is illegal and immoral because it misrepresents the product.
Selling stock, when you make it clear that your stock is worthless does not misrepresent the product.
And, again - note that Alice is not even required to make such a disclosure, when selling her stock to Bob. The assumption on the stock exchange is that as long as public companies are up front and honest about their financials, it's Bob's responsibility to not buy stupid, overpriced crap.
Selling stock, when you make it clear that your stock is worthless does not misrepresent the product.
And, again - note that Alice is not even required to make such a disclosure, when selling her stock to Bob. The assumption on the stock exchange is that as long as public companies are up front and honest about their financials, it's Bob's responsibility to not buy stupid, overpriced crap.