When Bill Gates founded Microsoft in 1975, the top marginal tax rate on personal income was 70 percent, tax rates on capital gains and corporate income were significantly higher than at present, and the estate tax was a much more formidable levy. None of that dissuaded Mr. Gates from pouring himself into his business, nor discouraged his investors from pouring in their money.

Yet he is now the latest affluent American to warn that Senator Elizabeth Warren’s plan for much higher taxes on the rich would be bad not just for the wealthy but for the rest of America, too.

Mr. Gates, the co-founder of Microsoft, suggested on Wednesday that a big tax increase would result in less economic growth. “I do think if you tax too much you do risk the capital formation, innovation, U.S. as the desirable place to do innovative companies — I do think you risk that,” he said.

Other perturbed plutocrats have made the same point with less finesse. The billionaire investor Leon Cooperman was downright crude when he declared that Ms. Warren was wrecking the American dream. Jamie Dimon, the chief executive of JPMorgan Chase, complained on CNBC that Ms. Warren “uses some pretty harsh words” about the rich. He added, “ Some would say vilifies successful people.”