Teddy Roosevelt promoted the income tax during his presidency. The theory being that it would be “more just” than tariffs (there’s a lesson there, somewhere).
His successor Taft supported a Constitutional amendment authorizing federal income taxes. The amendment was ratified in February 1913, before Wilson took office.
Wilson signed the bill which included the income tax in October, 1913. The top rate being an exorbitant 1%.
The camel got its nose inside the tent.
I think the discussion included the tax rate and no one could conceive of the rate ever exceeding 2%.