Well, they got a conversation started.
Most fish are purchased as impulse buys with Mom buying whatever color of fish that Junior fancies at the moment. As soon as Junior tires and the tank starts smelling, the fish get flushed. Mom chalks it up as a "lesson of responsibility" and sagely uses the experience to counter later appeals for a dog.
In Asia, fish are filleted alive, served still twitching to be dipped in wasabi-spiked sauces. World wide, fish are skewed though their gills and dragged along on strings though the water until their tormentor decides to quit fishing for the day.
And many LFS are gulags for fish, with filthy conditions, grotesquely inbred stock, and tatooed fish. Etc, etc.
So when one really thinks about it, these people have a point. I don't agree with them, but just sayin'.