eh, I just think the step for doing that to a dog is a little bit bigger than mistreating fish, but thinking about all the purse dogs, or dogs that are just chained up outside all day, I don't think either can really exhibit their normal behaviors and often live reduced lifespans as a result too. That's not even considering dogs who are actually abused. In most places there are laws against mistreatment of "higher forms" of life, and I think it's just a matter of lack of resources that fish don't get the same attention, since even mammal abuse has to be pretty horrendous before someone actually gets fines or jail time for it. Some people just suck, some people are ignorant and goodhearted, and some people start out with good intentions and then life gets the better of them.
kind of like
@Jamesthecat said, the older I get the more nuances I see in why things go a certain way. Big picture, it's hard to find good people (in any facet of life) - when you do, stick to them.