tax laws do not prevent the use of bitcoin. the might make it more difficult depending on your country and circumstance, but they don't prevent its use. agree about the de facto laws, or more like the arbitrary interpretation of existing laws. but like anything new, it takes a few court cases to clarify the interpretation. obviously if bitcoin does become the default currency then governments will start writing new laws as their tax income will evaporate. but thata a whole different conversation about the role government shoukd play