I don't care if someone is not paying taxes, good for them if they can avoid having the government steal their profits and stay out of jail. I don't even care if they're doing something the government deems illegal, especially if it's a victimless crime.
Regardless, I'd rather have the victims pursue the offenders through legal means (which, in a world without a government with monopoly on violence, will likely take the shape of multiple competing protection agencies) and victimless crimes not to be considered crimes at all.
I agree for some transactions you may want to exchange data and legal jurisdictions or setup a contract so that goods / services (+ future support) and money are exchanged safely and without scams - but that's irrespective from the means of payment.