Do people disagree with keeping budgies in very large cages (avaries)? Personally am happy for budgies and other similarly sized birds to be well kept in large cages, ensuring they get as much time to fly as possible, but I do not agree with them being kept in very small cages (you know the kind sold at pets at home).
I would never keep large parrots myself, but the difference in IQ and needs between budgies and say, African greys is very large. And I'm not saying that just because budgies are stupider than african greys they should be kept in poor(er) conditions, I'm just saying their basic needs are different.
Our budgies have a large enclosure (and there are only two of them (a non breeding male/female pair)). The female, Maisy can't fly well (we rescued her) but she enjoys short flights. Eno, the male is an accomplished flyer, and does so.
The thing about budgies is that even in the wild they fly only when totally necessary. For most of the day they sit on or near a food source and basically mess around: with each other, with their surroundings, and eat. Apart from that they really don't fly very much. This is very unlike Af greys, in that these birds fly for kilometres every day. I am only really going to agree with budgies being kept as pets because I know little about the natural behaviour of other small birds.
That is why I think that certain birds are OK to be kept as pets (although they aren't easy to keep: you need a good avian vet and some prior knowledge) and some most definitely aren't, which is when it becomes cruelty.