The government must stop taking its "eye off the ball" of economic growth, as uncertainty is hindering investors and companies, says legendary real estate investor Sam Zell.

The approach to income inequality in Washington is causing a problem, he tells CNBC.

"Wealth redistribution" policies are holding the economy back, Zell says. "I find it difficult to believe that you can have wealth redistribution and growth at the same time."

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Economist John Maynard Keynes talked about the "animal spirits" that get activated in the marketplace when things are going well. Zell sees little evidence of that now.

"I don't see any animal aspirations," he said. "I think we need to refocus our efforts on growth."

Fourth-quarter GDP growth was revised down to 2.4 percent Friday from 3.2 percent previously.

The Federal Reserve has a role to play, because its policy can affect the "levels of uncertainty," which influence the willingness to take risk, Zell said. "That's really what growth is all about."

But former Fed Chairman Alan Greenspan says income inequality is the 'most dangerous' trend in the nation.

"I consider income inequality the most dangerous part of what’s going on in the United States," Greenspan said at the National Association of Business Economists conference.

"You can see the deteriorating impact of that on our current political system, and you cannot talk about politics without talking about its impact on the economy."

The head of the International Monetary Fund also warned that rising inequality can damage economic growth and social ties, and may also cause political instability, Reuters reported.

"Rising inequality and economic exclusion can have pernicious effects,"said IMF Managing Director Christine Lagarde, according to prepared remarks, pointing to IMF research that shows income gaps can lead to slower and less sustainable growth.

"In the years ahead, it will no longer be enough to look simply at economic growth," she said. "We will need to ask if this growth is inclusive."

Meanwhile, the Fed should stop using the 2008-09 financial crisis as an excuse for our weak growth now, Zell, says.

Some experts expect the economy to rebound when the weather improves.

"You should see some pent-up activity show up in the second quarter of the year," Jacob Oubina, a senior U.S. economist at RBC Capital Markets, told Bloomberg. This year, "it’s a less-headwinds story rather than fundamental improvement in the internals of the economy."

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