Speaking of bubbles....
Why this is problem?
? ( I know most people think this as "printing money", but what is the difference of holding cash vs. holding US Government bond, they are all US government created monetary instrument) And the only thing Fed has done is exchange private held US Government bond with private held Federal Reserve Note. The action itself almost has no impact except banks now has no interest coupon from US Government.
Fed do this because people think it is printing money, so people will act the way Fed want them to. The action itself is almost a gimmick, pretend to do sth without doing anything.