But if the Fed hadn't bought the Treasury bonds, some other investor would've, just at a worse price. That's the thing about markets: participants are fungible, as is the money itself.
There's a big difference in dynamics between one firm giving money to another in a non-competitive situation (say, a union bargaining with a monopsony corporation) vs. a market of buyers trading with a market of sellers (say, the commodity or stock markets). You get efficient price discovery in the latter situation, you don't in the former. And the concern up-thread about the sheer scale of Fed purchases is that when the Fed becomes the only market participant, it starts to look an awful lot like the former situation, and market mechanisms break down.
There's a big difference in dynamics between one firm giving money to another in a non-competitive situation (say, a union bargaining with a monopsony corporation) vs. a market of buyers trading with a market of sellers (say, the commodity or stock markets). You get efficient price discovery in the latter situation, you don't in the former. And the concern up-thread about the sheer scale of Fed purchases is that when the Fed becomes the only market participant, it starts to look an awful lot like the former situation, and market mechanisms break down.