Earlier quoted context omitted.
It increases the information that makes its way into the markets and makes it more likely that the price reflects the what's happening in the real world. A world in which nobody bothered to check whether a company was actually producing anything would turn the stock market into a collective guessing game.
The stock market is a collective guessing game. These stories suffer from survivorship bias. For every investor A you hear about who did X and was successful, there are investors B, C, and D who also did X and were not successful, and don’t get articles written about them. There are also investors E, F, and G who don’t do X and may be successful or unsuccessful. Finding someone successful at stock picking and asking…
The hard part is not regressing to the mean, and consistently beating the market, which sure, nobody can do. But if I learn today that a stock is going to rise tomorrow, and I buy as much as I can, the stock will rise a bit today. So the market has become a little bit more efficient.
That I happen to then base all my subsequent trades on overconfidence and tossing darts doesn't retroactively invalidate that trade. You can even make a market more efficient on losing trades- you short a stock, it goes down a bit, but you spend more maintaining the short than the stock goes down. Then, the stock crashes after your short expires. Oops! But your prediction was still partly right, and that information was integrated into the price a bit earlier than it would have been without you.