Stock buybacks were once considered illegal, but the practice became legal during the 1980s. But it has only been in the 15 years or so that stock buybacks have become standard operating procedure for many companies – even some of the most venerable blue chip companies. Still, stock buybacks are still criticized for several reasons:
One critique of a stock buyback is that a company can use excess cash for a variety of purposes that contribute to its social purpose. These can include raising wages for existing workers, investing in research and development, or increasing capital expenditures.
The idea that a company might be beholden to its employees as much as, or at least in proportion to, its shareholders, is more of a philosophical debate.  A more fundamental concern is that stock buybacks may be too short-sighted. By putting too much emphasis on the next quarter, or the next six months, a company may be undervaluing its cash on hand and issuing stock buybacks that are too large, which can hurt shareholders and even the broader economy.
A third concern that economists have about stock buybacks is that, because repurchasing stock can have positive effects on a company’s balance sheet, a company may use a buyback as a way of covering up more serious issues. For example, it’s a fairly common practice for companies to borrow money to execute its share buybacks. But if that borrowed money is taking the place of actual cash, it can reflect that a company is using a buyback to paper over deeper problems.