Interesting that you mention Pugs as I feel the same way about them (and had a discussion about just those issues when out walking the dog earlier), and bulldogs too.
If all those genetically different species were functionally the same species we would see all sorts of hybrids in the wild, which we don't. We, in fact, for the most part see the opposite. A couple of hours from me are a few lakes that have 2 unique strains of Lake Trout. One strain occurs naturally in only one or two lakes, and no where else, and the other possibly only in one. In one of these lake is a population of the regular strain of lake trout that populates the entire country, and yet they don't interbreed, even though they are the same species.
I don't have a problem with people keeping flowerhorns, and realize that a lot of people who keep them aren't aquarists, in that they have no interest in other fish. The problem I have is with the instigators in the ornamental trade that use questionable techniques (hormones?) to create abominations, such as the blood parrot, balloon rams, angel rams, and all the other balloon fish, and then take the next step and dye and tattoo them. A flowerhorn at least looks like a fish (sort of). The other issue with hybrids is when they are sold as a species, sometimes unintentionally, and the customer is not getting what they are paying for.