The issue is that deciding not to pay your taxes means that the dogs are set on you. This is not a free society, unfortunately. Perhaps bitcoin will change all of this. I've been contemplating the idea of a shadow economy where people work remotely and anonymously, getting paid in an anonymous currency and completely circumventing the current economic and political systems.
A fundamental misconception of Bitcoin is that using Bitcoin as a currency will magically obliterate the Government's ability to determine income taxes. The government never has tracked currency for the purposes of determining income. They track transactions in whatever currency or assets the transactions are denominated. Thus, governments have been able to determine taxes since the days of barter, and they will continue to be able to determine taxes until long after Bitcoin is digital dust.