It was there for a fucking *great* reason: the failure to separate banks allowed them to act like casinos, inflating a giant market bubble that popped on Black Friday in October 1929, kicking off the Great Depression. Congress built the structural separation fence to keep banks from doing it again.
In the 1990s, Bill Clinton agitated for getting rid of Glass-Steagall. He argued that new economic controls would allow the government to prevent another giant bubble and crash.
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