I think the idea is just that BTC is property and in common law jurisdictions you largely have an inalienable right to dispose of your property how you want. It’s not really barter, in the sense that word is usually used, just that the gov’t cant usually prohibit you from, e.g., selling your lawnmower to your neighbor. Whether you have tax obligations or whatever thats a separate issue, but they cant typically prohibit p2p exchanges of property.