Your car analogy conflates scarce and non-scarce goods. A better car analogy would be that someone invents a way to create cars for $200 with 3D printers, and so everyone stops buying cars that cost 100x that much. "You wouldn't download a car" and all that. Of course, someone has to create the CAD designs or whatever, but that's a much smaller industry than all the manufacturing that existed before (so, of course, all the people who work in auto factories are upset that they've been made irrelevant).
I explicitly acknowledge the difference between scarce and non-scare goods in the above post if you could bother to read the second paragraph. The part you're leaving out in your 'improved' anology is that it might cost 10 years and ten million dollars to develop this $200 car.
Basically the great-grand-parent is saying that there's no rational or moral justification for someone profiting from innovation, because it's in someone else's self interest to take that innovation, and these two parties self interests cancel each other out to the exclusion of all other factors. I find that to be an extremely naive and simplistic argument.
