If you believe that, I have some ENE and WCOM stock to sell to you.
I am not saying there will not be any criminal activity. But the fact that there were criminal prosecutions at those companies is plenty of deterent. And prudent investors in those companies could have done due dilligence and gotten clues the companies were shifty and pulled their money out. The point is the free market of investors is better at sending and receiving signals of poorly run companies than the government. And in the examples you cited, investors did not have to be covered by the government.