All my daughter wants in this world is a dog. There's several reasons why I have to say 'no' to that - one is that I simply could not afford a vet bill if the cat and dog got sick at the same time. I could pay only one or the other..
It's hard to take good care of our pets on this budget - but we do without - pizza, fancy brand things, expensive internet, all kinds of stuff - to make sure the animals and fish get what they need because pets are more important to us than stuff.
I guess I'm leading up to saying that I don't understand parents who will allow a child a pet and then deny them what they need to take basic care of that pet. So they should do without pizza one week, maybe cut down cigarettes, buy homebrand stuff for a while, so they can buy the kid a tank/heater/good fish food... jeez, it's not the end of the world to give your kid what they need for their pet. Or why let them have it in the first place?? It's more damaging to all concerned to NOT allow proper care.
That said, whether or not a fish can be kept adequately in under a gallon is always going to be highly contentious issue. Even so, in my observation, it is the people yelling six ways to Sunday that under a gallon is just fine whom I very often see shortly after, posting in the sick fish forum...
It isn't fair that the original poster was permitted a pet, only to be denied what he/she needs to take ideal care of it. I bet you're doing what you can to make sure your fish is doing fine.
However, I think posting threads that cannot be anything but a source of divided opinion and kneejerk reactions is probably not a great idea. Better to ask "Hey, this is my situation, I cannot presently change that, so how can do my best with what I have?"
I guarantee more positive reactions. Less sour feelings.