Stock markets allow for price discovery. The market gives a verdict on what it thinks stock in a given company is worth, and it's there in public for all to see

Stock markets allow for price discovery. The market gives a verdict on what it thinks stock in a given company is worth, and it's there in public for all to see. They also allow liquidity. A public company can't stop you from selling your stake, or buying more. This is something you'd definitely value if you've ever been screwed out of equity at a startup.