I don't believe private investors decide they'd rather buy a yacht than invest their money just because a company bought back shares. More likely, the share buyback just moved money from a mature company to growth stocks or startups, which is exactly what should happen in a healthy economy.
Put another way...should Dinosaur Oil Inc use their profits to build another refinery even when they don't think it makes financial sense...or should they buy back stock, make their investors happy, and then be in a more vulnerable position when the investors turn around and fund Shiny Solar Inc?