No, you have to accept dollars because of legal tender laws.
Exactly. While one could use competing currencies (
Liberty Dollar, for instance, of course the feds busted them for "counterfeiting", even though no Federal Reserve Notes have a denomination with Ron Paul on them), the legal tender laws ensure that if you use the FRNs, you will get service, whereas you have a lower chance of getting service if you use a private currency. Thus, this gives the FRNs an unfair advantage, since Gresham's Laws says that under legal tender laws, one would be more likely to use the less valuable currency than the more valuable currency. If legal tender laws were abolished, and the FBI stopped raiding private mints on bogus counterfeit charges, then we might have competing currencies.