I've always wondered about this, but haven't dug into it - why is a poll tax unconstitutional, but the federal excise tax on firearms and ammunition not?

The 24th amendment.

>The right of citizens of the United States to vote in any primary or other election for President or Vice President, for electors for President or Vice President, or for Senator or Representative in Congress, shall not be denied or abridged by the United States or any State by reason of failure to pay any poll tax or other tax.

Well, there you go :)

Thank you. I'm surprised and a bit embarrassed to admit I was ignorant of the fact that it was clearly spelled out in an Amendment, but am happy to have rectified that ignorance.

Finally, a sensible argument.

I do think an ID that you need to have and is gvt issued should be baid by taxes. But noone likes those.