The stock market, much like capitalism in general, is useful if regulated properly, but the inherent corrosive nature of human greed on any regulatory system will eventually erode those regulations down and let this shit run rampant. There are genuine benefits to it, but they're buried beneath the sheer scale of wealth begetting more wealth at the expense of everyone else.
Part of it is that, to spite it being "gambling", it sure doesn't feel like there's a lot of losing going on with the biggest players. They don't seem to need to be as careful as you or I would need to be. It'd be one thing if it was fair gambling, but it isn't.