[natural selection as a man-made construct]
Darwin was quite familiar with the results of selective breeding of pigeons, dogs, cattle, race horses, and other domestic animals.
In the Galapagos he saw what were obviously finches that were somewhat specialized with respect to food, and that they had somewhat different beaks, seemingly designed for the foods they ate.
(One of) his "AHA" moments was when he realized what was going on: if a dog breeder only lets the smallest dogs reproduce, he eventually winds up with terriers and chihuahuas. If the most abundant food is nuts, we eventually wind up with finches with parrot-like beaks.
IN one case the bigger dogs aren't allowed to breed; in the other case, the finches with the duck-like beaks starve
What exactly is wrong with this?
There is nothing wrong with making the observations, recording them, and coming up with words like "natural selection" to describe what is happening. It just does not rise to the level of hard, empirical science, and it does not necessarily lead toward the wider conclusion some are inclined to draw that the history of life is best depicted as a gradual progression from simple to more complex biological entities.
I would even go further and say there is nothing necessarily "wrong" with positing this latter idea for biological history in an academic context. But it strikes me as stupendously arrogant to posit it as if it is beyond question or challenge, and to employ the legal system of the United States or any country to squelch views that may be contrary.
What's WRONG?
He'll end up with SMALLER dogs!