What event shifted public opinion away from a laissez-faire view of government towards a more activist view?

The correct answer to this is the event of:

"The Great Depression"

The Great Depression occured from 1929 to 1939, and was the most horrible economic recession in the history. It started after the stock market crashed on October 1929, which sent Wall Street into panic and erased millions of investors. This considerably hanged the popular view of government's appropriate role in the economy. The Great Depression convinced a lot of people that the government had a role in correcting for aggregate market failures and hence leading to a shift from Laissez-Faire view towards a more activist view of the government.