I'm not arguing that a redeemable currency is better or worse than a non-redeemable one. I'm merely pointing out that USD is fundamentally different from an IOU, because the US dollar is non-redeemable and an IOU is redeemable. None of this has anything to do with the status of USD as legal tender, which is something you brought up for reasons that elude me (it looked like you misinterpreted the term 'redeemable' to mean 'legal tender', that's why I was trying to clear this up).