By locking birds in cages, we've essentially denied them enjoyment for our pleasure—and isn't that the the textbook definition of cruel?
Birds are routinely denied two of their most fundamental natural behaviors — flying and socialization. Denial of these activities can cause physical and behavioral abnormalities including incessant screaming, pacing, head-bobbing, feather-plucking, and self-mutilation. Captive birds may also exhibit extremely low behavior, appearing to be catatonic. This is not the sign of a well-adjusted bird, it’s a sign of a bird who has given up.
Birds, if properly trained, can really bond with their human owners and make fantastic pets! They're not anti-social whatsoever and often enjoy the company of humans just as much as any bird. Tamed cockatiels, for instance, love being indoor pets!
If you want a pet that will bond strongly with you, a bird is a wonderful choice. Given proper training and socialization, birds can be every bit as loving and affectionate as a cat or dog. Many pet birds are inseparable from their owners, some even accompanying them on daily errands such as trips to the bank or grocery store.
That's a load of bullpucky. There's no such thing as a "tamed" or "domesticated" bird. These are wild creatures that humans breed and cage for their own enjoyment. Some species, like parrots (which people consistently point out as being great pets), can even outlive their human owners:
Parrots are also extremely intelligent and social—they have been compared to human toddlers in the needs of their emotional and social lives, but, unlike children, they never grow up. Birds are meant to fly and to be with other birds. Confinement in cages can lead to neurotic behavior, excessive screaming, feather plucking, self-mutilation and other destructive habits. As a result, very few people are capable of caring for the special needs of exotic birds or comprehend the seriousness of the commitment for the birds’ life span—20 to 70 years or more depending on species.
Let's be honest, people aren't going into the forest and caging wild birds. These are animals bred to be socialized in homes, and can offer mental stimulation and promote empathy in adults and children:
Pets fill the need to nurture someone. Pet birds are particularly good for this, because they require such a lot of personal attention and interaction with you, in order to be healthy.