I think you're misunderstanding the threat model. It's designed to protect unsophisticated investors from fraudsters, not from the investors themselves.
If that's the case, why do Pattern Day Trader rules exist? They seem to generally cover "protecting you from yourself", not from some third-party.
I don't think this is true. A clear example is startup stock-options. It is legal for the company to give you that as compensation, you historically get taxed for that compensation, it is legally mandated to get appraisal by a third-party company, but it is generally illegal to offer them for sale in the public.