No court has ever made any ruling remotely close to that, and since the first income tax authorized under the 16th amendment was progressive, it would be hard to argue that the original intent of the authors of that amendment wasn't to authorize progressive taxation.
Agreed. It would also be very hard to argue that the original intent of the author's of the 14th amendment was to declare that states must recognize same sex unions as marriage.
I hold that sexual orientation is one's own business, but marriage is between a man and a woman, with one historical variant being between a man and several women. That is simply the definition of what it is. That definition has no good reason to be changed, but it does have a bad one. In a free country nothing is stopping people from starting a cultural institution which honors or sanctifies same sex couples, but trying to simply declare that such institutions are marriages is like a small brewery selling its beer under the name Budweiser in order to make it more popular. I say the brewery should sell its beer under its own trademark and let its success or failure be determined by its quality.