Some people refer to the U.S. as "post 9/11" but a more accurate assessment would be "post constitution" it's debatable exactly when we crossed that threshold, but one would have a very difficult time arguing that our government still adheres to it's foundational document.
Therefore, the question is not whether something is illegal or legal, as those have been demonstrated to be arbitrary terms. If it serves the agenda of the bureaucracy, it will be deemed legal, as they are the ones that make that determination. The partisan system of politics dissolves the separation of powers between the branches of govt. If members of all three branches belong to the same party that is funded by "corporate persons", a uniform agenda can be pushed through regardless of the protections built into the system, as they have been effectively circumvented.
The points about tire taxes not infringing the right to travel, or newspaper taxes not infringing the right to free speech are not valid IMO. The 2nd amendment is the only one that guarantees the right to possess a physical object. Thus, to accurately compare a tax on "arms" to other rights, we mist be just as direct. Would a tax on speaking in public be unconstitutional? Would a tax on attending church be unconstitutional? Would a tax on moving across state lines be unconstitutional? If the second amendment were held to the same standards as the other enumerated rights, the NFA, GCA, AWB, and any other law that infringes our RTKBA would be deemed unconstitutional. Unfortunately, we crossed that bridge before any of us were born. As one of the leaders of this nation put it, the constitution is "just a goddamn piece of paper". We shouldn't be fooled into believing that it actually affords us any protections when it has been blatantly circumvented.