though the size of the loaches comes to mind... most new fish keepers will eventually get a larger tank or ridthemselves of larger fish in exchange for the smaller versions.
In best case scenerios.. if someone has the loaches for the period of time it takes them to grow to a foot...they will not mind getting a larger tank, they will want to and hence the size of the fish will help move them towards that decision...
I appreciate people are concerned of the eventual size of the fish in most tanks...reality is that most aquarist do not keep fish long enough to see true size potential in the fish they initial purchase..... so enjoy them while they are young...
I like and choose to believe that those concerned enough to be here are not "most aquarists". I fully plan of seeing every fish I purchase die of old age. Of course fish do die, but to plan on failure is to invite it.
That said, If responsibly kept and eventually responsibly adopted out I could agree with your position. The problem is that I see alot of people that go with bad initial advice with the best of intentions and they are eventually faced with frustrating choices which usually punish only the fish. See craigslist. I recently saw a 29G with an Oscar, 3 Clown Loaches, and a Pleco (all 6" +).