econd reason is that our social biology is extremely much more developed than in any other animal
You might want to read some of Frans de Waal's recent books, especially "are we smart enough to know how smart animals are?"
It is more developed, but by a smaller degree then you might think...
Most animal species kept in zoos perceive captivity as something good:
Do you have any evidence for this claim, as this is something impossible to infer directly...
Leave a zoo animal free, in most cases, would be likely leave an human abandoned in the forest or in a moutain, far from any civilization.
No, it would be like leaving a small child who has always been cared for, that did not have to do anything and without any real sense of danger free in New York City. He would have to learn a lot really quickly or things end up badly...
once filled all their social and welfare needs in a way that they can be feel good inside their enclosure, is something bad. Obviously always are exceptions (species whose needs are too difficult or impossible to replicate in captivity, for example whales, humans, obligated migratory species, deep sea species, etc),
But still we keep a lot of species where we cannot replicate all their welfare needs, we are keeping a lot of migratory birds in aviaries of less than 20 square meters and migratory birds like cranes cannot even fly... We can recreate enough of the basic needs to keep animals alive, get them to breed and nowadays also enough to fulfill behavioral needs, but that is still very much a work in progress...
Personally I do not think that many animals, like hoof stock, know they are held captive. But I am sure great apes are very well aware of the extent of their "freedom". The problem with this freedom debate is that in the wild most animals are also not free, either because they have a certain territory or whether they live in a "landscape of fear". So movements in the wild are also limited, but still much less then in zoos. For example chimpanzees have territories over 1000 times the size of zoo enclosures (and which much more height as well...), so they are able to show behavior that is impossible in almost all zoos, such as the splitting of one group into several smaller groups that go on foraging trips. For obvious reasons we also do not provide them with a rival group to interact with. And in zoos searching for food, normally a main activity, is something that takes much less time... The question whether freedom is also a fundamental right for animals is hard to answer with regards to zoo animals, as I personally think even animals aware of the limits in their enclosures can be perfectly happy and would maybe not be happier to have "complete freedom"...
Overall the main difference between the wild and zoos is that the freedom is limited in different ways (fences vs. territory/predators/food availability), so broadly spoken no animal is free at any time, but overall wild animals have a broader choice of where to be, which is also freedom in some way... Imo the question is more whether it is ethically correct to limit this type of freedom to a certain level and I think that in most cases we can reach a certain threshold level (which differs between species) at which we do not limit the 2nd type of freedom too much, but this differs again between zoos... I think we all agree that it is ethically bad to keep chimpanzees solitary in 12 square meter cages, but having them roam a wooded area of over a hectare in a larger group is acceptable.
For some animals we will never reach this acceptance threshold, large whales are an obvious example (though it could theoretically be done with infinite resources...). What bothers me more is larger birds of prey, which often cannot fly for more than 5 seconds in zoos, whereas they spend large time in the air normally showing a whole array of behavior from gliding to mating dances... We can keep them alive very well and many species have excellent breeding records, but whether we reach their threshold, I am not sure...