The 1929 crash was not merely a "fluctuation."
Misguided policies will exacerbate a problem, but a market crash is a social shock that knocks the confidence (often misguided confidence) from an overheated economy. Deleveraging is a natural a consequence as...a hangover after a drinking binge.
IMHO, the crash on its own would have caused a recession or a mini-depression. It took bad government policy (Smoot-Hawley, etc.) to turn it into the Great Depression. In fact, anticipation of Smoot-Hawley might have helped cause the crash, then made the economy worse after being enacted.