The problem with your analogy is that a potential swimmer's total knowledge of the water, the difficulty of swimming and so forth isn't held by someone who materially benefits from their ignorance and could materially benefit from exploiting that ignorance.
Caveat Emptor is a fine base-line. But practical experience has shown us that in certain sectors it's not sufficient. Snake oil salesmen can ruin a market by destroying the public's trust.
So it is with investments. SEC rules are generally [1] built on the practical experience of how the market operated without them.
We threw Glass-Steagal away -- an expensively won bit of knowledge about the shortcomings of the 'invisible hand' when it came to people gambling with others' money -- on the assumption that intelligent self-interested experts wouldn't do exactly what they -- almost to a person -- then did. I can't fathom being so eager to repeat that mistake while we're still knee-deep in its debris.
[1] I won't dare use a universal; but I've yet to see a rule that wasn't created as a reaction to a problem in the market. That said, I'm far from an expert on the matter.