But, there is no Constitutional prohibition upon taxing firearms.
Taxing the exercise of the right to keep and bear arms with the intent to restrict said exercise violates the constitution every bit as much as so taxing the exercise of the right to an abortion.
You may be right, but you may also be wrong. Any Constitutional scholar will tell you that there are two kinds of rights protected by that document: Enumerated and implied. Only those rights specifically mentioned in the Constitution and its Amendments are enumerated. All others are implied from the overall tone of the history of the formation of the United States, the Declaration of Independence and whatever other source from common law or precedent which can be extracted.
For instance, Roe v. Wade was not a taxation ruling or a ruling on an enumerated right. There is no Constitutionally protected right to have an abortion. There IS, however, an implied right to privacy which the court found in the due process clause of the 14th Amendment and THAT is what they ruled upon: That the state had denied "Roe" her implied right to privacy.
Now..let's take gun laws. While the right to keep and bear arms IS an enumerated right in the Constitution, The People of the various states have the implied right to regulate that enumerated right however they see fit, so long as it does not totally deny a citizen the right to have a gun. The SC said so in both Heller and McDonald. In other words, there is no Constitutional prohibition on gun control short of a total ban and, since the states have the right under their own Constitutions and the Federal Constitution to impose taxes, the right to tax firearms is implied.
Moreover, most of the states considering levying heavy taxes on guns and ammunition are staying their actions as "sales taxes," the 2nd Amendment issue might not even come up.
The point is that I think they CAN do it and the push for higher tobacco taxes paved the way for it. Worse, as tobacco restrictions grow worse and more draconian, it continues to provide a legal precedent for doing whatever the government wishes to do against any product or behavior it can dream up. Never underestimate the legal authority and power of precedent.
That's why these new proposed higher cigarette taxes need to be opposed as a vehicle for preventing the very same thing being done to guns.