Again, a little devils advocasy, but I do feel this way.
Relatively speaking, to me a 12" oscar in a 55 is about the same as a goldfish in a bowl, maybe worse.
Survival, is one thing, but actual livability is another.
When you compare the awareness that an adult oscar has of its surroundings, and even the room outside its glass prison, with the none awareness of 1" goldfish, the cruelty quotient becomes painfully apparent.
Seeing that goldfish reach almost 10" or larger with enough space and are very aware of people outside the tank and knowing where the food comes in (mine know exactly) kinda voids the statement. A 1"oscar probably isnt much aware either.