I don’t think you now the meaning of the word “legal”. Income taxes are perfectly legal and it’s been proven every time someone tries to disprove it.
It's what the taxpayer the article is written about is asking the Courts and IRS to define (i.e., are wages income?). He cites a case in the past were the court ruled that it wasn't income, because your labor is considered an expense to you.
I'm no expert in these matters, just trying to clear up what's being presented in the article linked.
I pay all of my taxes, because it will be held against me and enforced IF I don’t. I do not believe income tax is legal, nor has it been proved that it is legal.
I do expect that my State will drop the income tax, along with other Southern States. I know for a fact that part of the reason the Legislature is promoting dropping the income tax is because it is “illegal” to tax that money twice.