they think it will live better but in many cases the fish either dies from starvation and poor water (lots of pollution = death) or they take over the ecosystem and destroy everything else in their path. I generally equate it to setting humans free into our natural habitat. For some reason most people don't like the idea of getting dropped into the African grasslands to fend for themselves, free of the constraints of civilization and the "silly laws" that govern us (like, oh, i don't know, laws against putting animals into the wild who are not from there....)
I think in the past week I've refused sale of fish to at least 6 people because when I was describing water changes and ammonia the answer was "well who cares, its just a fish right?" "i'm sorry sir, I think you should shop elsewhere for your fish"