The tax as Congress wrote it was not considered unconstitutional then. There were no legal challenges to it. And as a matter of fact, the Confederate Congress enacted an income tax as well. Was it “unconstitutional?”
LOL! It was unconstitutional. The SCOTUS ruled it unconstitutional. There is a reason why nobody did it before and nobody did it again until passage of the 16th amendment. Did the Confederate government do things that violated the Confederate constitution in order to fight the war? Yes!