Earlier quoted context omitted.
At least in the case of Bernie Madoff, the SEC can say "no, it is illegal to run a ponzi scheme and in this case it should say what law the exchange broke to make it valid
They offered an unregistered security for sale. That is against the law.
And let's not ignore the fact that these exchanges have done this right out in the open for around 10 years now. Coinbase even had their IPO approved by the SEC. So it's very clear that the SEC treated this as legal for a decade before suddenly changing their position. This seems incredibly dishonest to me.