I don't think laissez-faire economics fell apart and led to the catastrophe which became the Great Depression. It's a common misconception that under-consumption and a stock market bubble caused it, but I think it was caused by the Fed responding by shrinking the money supply and the Hawley-Smoot Tariff Act halting imports that compounded a normal recession and turning into a larger problem.
Keynesianism, from the horse's mouth, is not a long term solution to economic problems. Keynes himself talked about how his theories were insufficient for forecasting long term economic growth. Unfortunately, we've fallen into the trap where we've lowered rates and accumulated debt to the point where it'd be dangerous to normalize the our monetary policy. We provided stimulus with no plan on paying it off during our most recent period of economic growth. Later on, Keynes even expresses that he started believing more and more in the invisible hand theory pushed forward by Adam Smith to better explain economic behavior.
I've always found Austrian economic theory to be more representative of the economy, as it encapsulates both supply and demand better, but that's just my opinion.
