Here's the real reason the Fed will taper QE: Pro

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Noted Nomura bear Bob Janjuah believes he knows the reason why the Federal Reserve will begin pulling back its easing program, and it's not about unemployment, inflation or anything else directly related to the economy.

Instead, he believes the central bank is worried that it is creating an asset bubble that will only get worse if it keeps following the current path.

"The Fed is NOT going to taper because the economy is too strong or because we have sustained core (wage) inflation, or because we have full employment—none of these conditions will be seen for some years to come," Nomura's fixed income strategist said in a recent missive to clients.

"Rather, I feel that the Fed is going to taper because it is getting very fearful that it is creating a number of significant and dangerous leverage driven speculative bubbles that could threaten the financial stability of the U.S. In central bank speak, the Fed has likely come to the point where it feels the costs now outweigh the benefits of more policy."

(Read Now: For Some, Fed Can Start Tapering NOW)

Janjuah's assertion is important because it would make a critical departure in thinking for the Open Markets Committee, which concludes a two-day meeting Wednesday.

Ostensibly the Fed has two goals: To maintain price stability and generate full employment.

However, its $85-billion-a-month bond-buying program's principal accomplishment has been to push up the stock market.

Since the Fed announced the third round of quantitative easing in September the Standard & Poor's 500 has gained more than 12 percent.

(Read More: Every Major Asset Class Is Overpriced: Analyst)

But job gains have remained modest—the unemployment rate ticked up to 7.6 percent in May, well above the Fed's 6.5 percent target rate before raising rates—and inflation is tracking at about 1.4 percent, well below the 2.5 percent target.

Worse, gross domestic product gains are almost certain to register below 2 percent for the second quarter after a lackluster 2.4 percent growth in the first quarter.

A tapering, then, that comes before a stronger economic recovery likely would rattle markets.

Finally, the Fed has a rather uncomfortable example to follow in Japan, where promises of accelerated quantitative easing were greeted with enthusiasm at first, only to see the Nikkei stock market fade badly after the initial euphoria.

The idea that the QE might be creating a bubble was first broached, in an indirect manner, during the last Fed meeting, when minutes indicated that some members were concerned that market expectations had grown.

(Read More: For Some Areas, the Fed Taper Already Has Begun)

"At least some members of the Fed may be worrying about the future of the Fed and the U.S. if they persist with treating emergency and highly experimental policy settings as the new normal," Janjuah said.

Amid a climate of "dangerously loose global central bank policy settings, increasing complacency towards risk and blind faith in central bank 'puts' amongst investors," Janjuah correctly forecast that the market would make a new high this year, though he expected it to happen in the third quarter.

Now he sees the groundwork being laid for a correction in late 2013, or early 2014, that could knock the market down 25 percent to 50 percent.

He believes the new bear market will happen after stocks churn around a little and get some dip-buying action before having to confront low economic growth and a market that soared on speculation.

"It depends on who says what, and on the levels of extreme speculation and leverage. In other words, did we collectively learn our lesson from the events leading up to and including the global 07/08 crash?" Janjuah said. "My 25-plus years in financial markets lead me to believe, sadly, that the answer is almost certainly NO."

By CNBC's Jeff Cox. Follow him @JeffCoxCNBCcom on Twitter.