From the peak of the dot-com bubble in March 2000 through March 2010, the S&P 500 was down 24% — a crippling stretch of returns that money managers cite as a prime example of a “lost decade” for markets.

Some on Wall Street seem to think another decadelong drought could be coming. Warnings of anemic returns ahead for the S&P 500 from top forecasters, including Goldman Sachs’ David Kostin, Bank of America’s Savita Subramanian, and Morgan Stanley’s Mike Wilson, have emerged over the last couple of years.

The key driver of their arguments is that starting valuations are historically high. The Shiller PE ratio, which has had a strong track record as a predictor for 10-year subsequent returns, is…