Income tax is theft, no matter what entity is responsible. This reminds me of the argument democrats (read statists) love to use when they encounter someone defending state's rights. They cry racism and all that nonsense. The Bill of Rights must be respected and upheld by governent at all levels. it should have been common sense that the Bill of Rights when created would by definiton make slavery immoral and illegal. The problem wasn't the Constitution it was the societal norm at the time.
For a good explanation on the 16th Amendment I suggest watching Aaron Russo's America: From Freedom to Fascism. In it he interviews many people with expert knowledge on these cases, particularly the Eisenhower vs Montgomery case. The Supreme Court has determined more than once that the Federal Gov't and the IRS are not granted any new taxing authority from the 16th amendment. Furthermore it has defined income as "gains or profits from corporate activity"