If a politician can convince you that he can fix income “inequality”...
and you go for it, realize it or not, you have just made him king. Because now he gets to decide how much you have, and how much you get to keep. With one move across the chess board he now owns it all.
Ratifying the 16th Amendment had the same effect. If the government can, by fiat, declare that a portion of your labor belongs pre-emptively to it, then you are nothing more than a slave for that portion of your day you labor for the government's profit. If the government can, under force of law and threat of violence against your person, lay claim to your property, you are no longer a free man. And if the government can decide that your "obligation" to it is 10 percent of your income, then it can just as easily decide it's 11 percent. Or 50. Or 100.
Any tax against property, whether it be personal property, real estate, or income, is inherently socialist because it declares that your property does not belong exclusively to you but to the Collective in some portion.