In fact, it's required for any market to exist in the first place. Without regulation the concept of ownership goes out the window. "Free markets" would look like anarchy... and exactly as you lay out in the river analogy it would be utter chaos with everyone acting in their best interest like "damn the consequences!" - it's human nature.
Sorry if I'm coming off as abrupt here - I'm aggressively agreeing and building on your point... IMO the markets require regulation when all is said and done. People who point to a "free market" often do so to shield themselves from the same regulations/rules that are designed to keep the markets afloat just like Pelosi has done here. It's gotten to the point that the words "free market" are almost always a sign of a bad faith argument.