The answer as to when some portion of the economic output of the country became ours to decide how to allocate is when a majority of taxpayers approved of it, including some fantastically wealthy folks who earned their money. Those are the breaks of living and doing business in a democratic country.
When the question begins with "Since when", I would expect the answer to involve a date. which I believe to be 1913.
The gist of the question was when the default mode of taxation changed to be for social engineering. That answer, of course, is much more complicated.
The point of the question, of course, is that the tax code is a monstrosity and intellectual abortion and to argue that it's broken, but only in these small areas, is to engage in the same idiocy that created the monster in the first place. To understand "when" -- it's roots and history -- is to understand why bickering over details is specious.
Since when did the entire economic output of the country become ours to decide how to allocate? Did I miss the revolution?