Governments hate it when you succeed at escaping their tyrannical reach and so we have been witnessing extensive efforts by the feds to curtail tax dodging and avoidance. This has led to some considerable pressure exerted on banks in Switzerland, Lichtenstein and other places with serious bank secrecy laws, to release the names of those who bank there hoping to escape the IRS. (The U. S. government wields not only military might!) Extorting money from the citizenry is the bread and butter of governments. No serious effort has ever been made even in America to find and implement ways of funding the legal system without using extortionist methods. Yet, how could one have an unalienable right to one's life and liberty and such while government puts a gun to one's head saying, "Your money or you go to jail"?
Tax resistance may be morally defended on grounds nearly identical to resisting any kind of aggression against oneself. If one is accosted on some city street and threatened, one has the right to defend oneself. The right of self-defense is derivable from the basic right one has to one's life, one that rests on one's nature as a human being as a moral agent. If one carries on in one's life peacefully and is nonetheless attacked, one is justified – has the right to – resist. This also holds if the attack is aimed at confiscating one's resources, even if one misuse these – wastefulness may not be criminalized in a free society unless it involves dumping, imposing it on others, as in pollution.
Government sanction of conscription may, even ought to be resisted. Draconian cases could be cited here, involving slaves or concentration camp victims taking measures to escape. There is no moral doubt about whether resisting being subjected to these is ethically justified (although in nearly all such cases government apologists defend themselves via either the doctrine of implied collective consent or invoking some "greater good")! The gist of the errors of such systems can be seen in the Declaration of Independence where instead of governments, it's individuals who have sovereignty. Or, in other words, instead of divine rights for monarchs, it's individual human beings who have basic, unalienable rights, including to their lives, liberty and property (the term Thomas Jefferson used in an early draft based on the Virginia Declaration of Rights, which referred to "property and pursuing happiness.").
Taxation, which is extortion, has no place, any more than serfdom, in a just legal order so whether it's ethically justified to dodge or avoid it should not pose an insurmountably difficult moral problem. (There are, of course, considerations as to the proper means by which tax laws, as others that are unjust within a substantially just system of laws, would need to be resisted.)
What we face here is akin to what confronted abolitionists in the era of chattel slavery who were often urged to refrain from using radical means by which to resist. Arguably, one size does not fit all in how oppression of any kind ought to be resisted, opposed, combated, and so forth. Different victims could be justified in taking very different steps to counter oppression, including taxation. For some it would be most appropriate to make use of the available political processes, for some other means could be best. Taxation could, for some, be a minor although impermissible imposition, especially if they are wealthy enough so it makes little difference to the way they choose to live their lives. The context is relevant to how one is justified in addressing oppression. (For a simple example, if one is a large, powerful individual then being assaulted could be nearly inconsequential and not worth spending the time and resources to resist.)
Although there could be variations in how one ought to resist (dodge, avoid, legally contest, etc.) taxation, the answer to whether those subject to the institution are ethically justified in making the effort to resist it is in the affirmative. Yet, as with all matters of conduct involving other people, a sort of moral due process is required. One may not resist a trespasser by killing him and that kind of consideration would apply in how one goes about resisting an evil such as taxation.
In any case, the often voiced objections to tax dodging and tax avoidance are without merit.