“”or that our “money” is really a negotiable security of no set value, and that the halachas apply only to the sorts of money they had in the past, which were coins with intrinsic value (paper money, and in particular paper money backed only faith in the government, is a new invention). “””
if there is such on opinion( that there is no problem of ribis with our government created money), it is certainly a minority opinion. I have never seen this mentioned in any thshuva or discussion of ribbis questions. Perhaps I just missed it, but surely it is not taken into consideration in any of the discussions I have read.