Your troll is worthless. There is no physical-object analogy, but one is coming: I copy the CAD design for a piece of plastic furniture being sold at huge profits. I then use my 3d printer to produce the same furniture at a slightly lower price than the original, and offer a free download of the CAD with it (the originator charged a nominal fee to pay for his server.) Since the CAD file is GPL licensed, perfectly within my rights. To continue business at his higher price, he may have to start competing in other ways: offer a warranty of basic function, have better availability, guarantee replacement turnaround, etc.
So then we both succeed in our various niches. But I find a way to improve the design and therefore more durable printed furniture. The originator is within his rights to copy my improvement back into his product.