I don't know if anyone has ever argued that the markets are bulletproof.
Should we not have speed limits because traffic accidents still exist in spite of traffic regulation?
No, but we also shouldn't imply the main reason accidents occurred before was because there were no speed limits.
I don't think anyone is arguing that lack accredited investor requirements was the main reason for the crash of 29, just that it's one of many common-sense regulations put in place to prevent a repeat of the worst outcomes.