QE2はインフレ率の低下を防ぐため

と、声明文で言っているわけですけれども。
Federal Reserve Board - FOMC statement

Consistent with its statutory mandate, the Committee seeks to foster maximum employment and price stability. Currently, the unemployment rate is elevated, and measures of underlying inflation are somewhat low, relative to levels that the Committee judges to be consistent, over the longer run, with its dual mandate. Although the Committee anticipates a gradual return to higher levels of resource utilization in a context of price stability, progress toward its objectives has been disappointingly slow.

The Committee will continue to monitor the economic outlook and financial developments and will employ its policy tools as necessary to support the economic recovery and to help ensure that inflation, over time, is at levels consistent with its mandate.

FRBの2つの使命とは物価と雇用の安定のことです。
その使命を達成するにはインフレ率が低い、それが問題だと言っていたわけです。
デフレでは当然ダメですから、デフレ回避のための量的緩和と見ても良いでしょう。
経済について理屈だけこねくり回して実証が何もない人は信用できませんね。
日銀は関係なかった！： デフレの真犯人 ―脱ROE〔株主資本利益率〕革命で甦る日本、北野一 : 金融日記