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!
Really? When. Did Lincoln ignore the Supreme Court? When did the Court rule the income tax unconstitutional. And as I recall, Justice Roger Taney, who hated Lincoln with a passion, was Chief Justice then, and his court never took up the case. Why was that?