Ray Dalio's hedge fund, Bridgewater, just put out a note suggesting the the biggest worry for markets should not be about the Fed tapering quantitative easing. It should be about the diminishing effects of QE.
The first point is relatively straight forward. The Fed has said it will slow and eventually cease its bond buying program when the economy shows signs that it is strong enough to withstand a removal of QE. This should mean that the taper shouldn't be a big deal: it will signal a removal of support for the economy at the same time as signaling that the economy no longer needs the support. Which is to say, we'll be transitioning from federal stimulus to market-generated stimulus.
So what happens if things don't go as planned? If the taper is premature or the economy subsequently contracts, the Fed should be able to turn around and reverse the taper. That is, restore QE or even increase it. So, again, the taper should be basically a non-event. Or, at most a temporary blip in the recovery.
The real worry, according to the folks at Bridgewater, is that further bond buying might just not work. QE might be close to the limit of its effectiveness.