These mandates are, of course, subjective and vague enough to be interpreted a variety of ways whether you view 'investors' as institutions, households, individuals, etc... What you define as 'fair/orderly/efficient', and what meaningful 'capital formation' really is.
When SEC approved Enron's change in account reporting practices from historical cost to mtm, I would argue that the SEC failed it's mandate to protect investors by allowing disingenuously optimistic instrument valuations. You could argue that eventually the SEC fulfilled its mandate by recovering much of the misappropriate funds, but it's hard to say they didn't also facilitate the disorder in approving these instruments given how that story concludes with a corporate collapse and flurry of regulation...