Stock buybacks provide at least one useful service. They allow companies that made the mistake of moving moving to a publicly traded company, undo that mistake and revert to private ownership.
There are at least a few examples of companies that were at one point declining, and arguably failing, under shortsighted shareholder leadership, and once the company reverted to private ownership and they could look at the long term again, turned things around to become effective companies again.
(The Dell computer company is one that sticks in my mind.)
I personally think the problem here isn't stock buybacks, it's that we allow easy trading of stocks(and all the more speculative shit that's really really sketchy magic money on paper that goes on) on an open market at all. The point of owning stock in a company shouldn't be looking to see how you can turn it around and sell it for a profit as quickly as possible, it should be as a share of earned profits and voting rights to help steer the direction of the company in order to help increase those future earned profits.
I'm not saying a certain amount of trading is wrong. But once you buy stock in a company, you should be locked in with the fate of that company for a certain amount of time just to guard against people doing sketchy shit like intentionally running a business into the ground for short term profits and the false appearance of value.