It's not only presumptuous to say "if someone's not rich, they must not be smart enough to invest", it's a self-fulfilling kind of thing, isn't it?
Nothing prevents people from gambling in Vegas. So clearly these laws are not about protecting fools from their own foolishness. No, the laws are about only one thing: making sure that the people who are in charge of the economic system, stay in charge. And it's not just these SEC laws, there are a wide variety of laws that secure the elite from competition by the peasants.
Whenever someone claims they're keeping you from doing something for your own good, who pretends to be your parent, they really are your master.