The thing that's always bugged me about proof of work systems is that there's no reason to assume mining power won't become concentrated into the hands of a few

The thing that's always bugged me about proof of work systems is that there's no reason to assume mining power won't become concentrated into the hands of a few actors. In fact, if (1) there are economies of scale in mining and (2) miners are rational and only work when they expect a positive return from mining, it seems like you'd expect mining power to become concentrated. (Of course today most miners operate at a loss, but I see no reason to depend on that.) I'm kind of a Bitcoin skeptic because I don't think you can build a trusted currency on top of a system with flawed economics like this.