Banks, when venturing into risk investment are actually playing with Deposit Insurance money, your tax money.
A real bank job is to loan money, not invest money. They examine the future of successful business presented by the business and determine can they utilize the loan to increase sales and profitability. At the interest rates banks charge they cannot afford to take risk of investment.
Only people that can afford a loss, as defined by a credited investor by government rules, are allowed to invest. Banks are not supposed to take losses as that would mean they could not pay back depositors. If they cannot then the government steps in. Is that what you want?
Glass-Stiegel law before and the Dodd-Frank laws are meant to keep the banks in the banking business. Perhaps the people wanting banks to cross the investment line should be playing with their own money, not government money.