Earlier quoted context omitted.
It's more interesting to me why we have a seemingly obvious belief that pump and dump schemes (which are effectively a sort of coordinated social phenomenon rather than a material movement) should be regulated. Begs the question: what is the "point" of the financial system, considered as a kind of bounded game, and why is that interesting to the state as an institution?
I'm no political philosopher, but I'd say, for example, the Preamble of the U.S. Constitution says the government's purpose is to “promote the general welfare." Phenomena like bank runs harm the general welfare, so the government has an interest in preventing or mitigating them.
But if we look at other sorts of more complex financial instruments, the sort of thing that's inaccessible to an average citizen, then why are they protected by the state as well? The obvious answer would be "well, banks invest in complex financial instruments, and the state wants banks to be protected". But regulating financial instruments isn't necessarily the only way of ensuring that the banks' service to their customers remains stable, it's just one possible path.