[rlucas]

Put another way, in an information-theoretic view of markets and money: stopping the yields from going up would make it more difficult for investors reliably to gauge how safe it is to lend money during a time of economic stress.

It's also not a scaling function (reduce everyone's cost of borrowing by 10%, say). There's a floor so you get a clipping effect.

The Fed's intervention is like the CD mastering Loudness Wars.