That is a heavy unpacking.
We'll start with the puppy mill analogy. The large fish farms which farm to supply ornamental fish for the huge pet trade are not really equivalent to a puppy mill.
Although there may be well tended breeding facilities for dogs, there is a difference with the "puppy mill" terminology. I have never seen evidence of a sanitary, neat and tidy puppy mill - usually poor animals in a tiny (often wire) cages and little care, human or animal companionship with little medical care.
Large ornamental fish facilities make all their money in breeding and selling thousands, if not millions of fish and aquatic creatures, and the larger facilities have huge filtering systems to keep water cleaned and checked. And a very careful method for keeping fish alive and in good condition or else they can't make any money. It is really big business for many of these.
But you are right that these fish aren't raised in a "home" like where their species came from. If you look through information, written word, video, pictures, about where specific fish come from it is easy to see how they might like to be kept.
The environment to which certain fish came from originally will help the fish feel more happy and less stressed. In an aquarium we usually try to make our pets happy and get them caves, branches for cover, certain pH or tannins in the water, the correct pH and water conditions to which they are most content in. Because we care about them.
But if people only have a puppy mill to make money, or keep fish only to make money, or someone is overwhelmed by the amount of work they have in keeping them, the animals suffer.
Anyway a aquarium keeper can get tired of their fish and let them suffer as well.
Generally we love and care about the pets.
Before I knew Cory catfish like friends because they are social fish and enjoy the safety feeling in numbers, I had only 1. It wasn't fish abuse because the tank was cared for.
So perhaps some people give information based upon how the type of fish would be most comfortable. There is a great deal of information based upon actual keepers, scientists and fish enthusiasts.
Having 1 Cory is not the ideal way to keep them - it is a fact, based upon experiences and seeing them in their natural habitat. My fish seemed content, curious and sociable with the other fish and didn't seem to suffer.
After I got a few more though, he was even more "happy", behaving as a part of the group and chasing, following and nuzzling the others and laying on them, etc.
As for all the bad information out their, sometimes it is just misinformation. Sometimes it is because new information was found out and the old information is still there as well.
Usually some fish are group fish, some are very bold, some need to be kept alone due to aggression issues.
An aquarium is similar but not exactly like a river, lake, stream.
This leaves the information up to you to double check and verify from more than one source.
You can never know every thing about keeping fish, or know too much about the fish you keep as new information comes up and you can find different fish to try in your tanks.
So it is true people who care about their pet / fish / animals want the best for them.
That is why I share information that I know and learn about and share my experiences with others. Because I want other people to have the basics and extra information to keep their fish the best they can be kept.
So welcome to the community. I hope you want to keep your fish in the best possible way, and can be here to learn and share your experiences and help others!
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
Start here - Aquarium Advice Article
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves