thief because their win was built on the losses of everyone else who bought lottery tickets?

Both the hedge funds and Reddit movement are doing the same thing, they are engaging in speculation. The difference is this time a couple hedge funds are the losers in the speculation game. Is throwing one's life savings into a stock for a company that is likely overvalued a good idea? No, it isn't, it is a huge gamble. But it isn't anything new, rampant speculation in financial markets has been around for hundreds of years.