'They are just doing stupid things': Billionaire investor Leon Cooperman warns the rise of Robinhood traders will 'end in tears'

· Billionaire investor Leon Cooperman says the way amateur investors are piling into the stock market is bound to "end in tears."
· Markets have seen a boom in day traders using platforms like Robinhood to buy stocks in recent months, helping boost US indexes.
· That's likely to come tumbling down, Cooperman told CNBC this...