Harvard economist Martin Feldstein is not a fan of the Federal Reserve's massive easing program, which includes near-zero short-term interest rates and a $4.5 trillion balance sheet.

"The Fed's unconventional monetary policies have created dangerous risks to the financial sector and the economy as a whole," he writes in an article for Project Syndicate.

"The very low interest rates that now prevail have driven investors to take excessive risks in order to achieve a higher current yield on their portfolios, often to meet return obligations set by pension and insurance contracts."

The result?

"This reaching for yield has driven up the prices of all long-term bonds to unsustainable levels, narrowed credit spreads on corporate bonds and emerging-market debt, raised the relative prices of commercial real estate and pushed up the stock market's price-earnings ratio to more than 25 percent higher than its historic average," explains Feldstein, chairman of President Reagan's Council of Economic Advisors.

The 30-year Treasury yield fell to a record low in January. And Robert Shiller's cyclically adjusted price-earnings ratio for the S&P 500, which includes 10 years of earnings, now stands at 27.3, a level exceeded only in the pre-crash periods of 1929, 2000 and 2007.

Meanwhile, the Fed dropped forward guidance from its policy statement Wednesday, meaning there's a chance for an interest rate hike as soon as June. But many economists don't expect the central bank to move until at least September.

That includes Feldstein. "My own best guess is that they will start to raise rates in September, and that the federal funds rate will reach 3 percent by some point in 2017." The Fed has kept its fed funds rate target at a record low of zero to 0.25 percent since December 2008.

"The FOMC [Federal Open Market Committee] members must recognize that they cannot postpone the increase in interest rates indefinitely, and that once they begin to raise the rates, they must get the real (inflation-adjusted) federal funds rate to 2 percent relatively quickly."

Chris Rupkey, chief financial economist at Bank of Tokyo-Mitsubishi UFJ, tells Bloomberg that "the economy has dug a deeper hole and will take longer for growth to bounce back above trend." GDP growth totaled only 0.2 percent in the first quarter, the government reported Wednesday.

A June rate hike "is on the table, but it's a long shot now," Rupkey argues.

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