'Dogs and cats are fine, fish maybe, and snakes and other more exotic animals probably not.' That's about as close to a consensus as we have for the domestication of animals, but they are judgements largely based on history and tradition and imply that freedom and space are more important to some animals than others.
Wittgenstein famously said that 'If a lion could talk, we could not understand him'. He meant that animal's experience of consciousness is completely different to our own and will always be impenetrably alien to us. That even if they could speak and we could translate their Lionese, it would not mesh with our communications and understanding of the world. He might not have it totally right – various animals' ability to convey messages and experience apparently quite human feelings of excitement, enjoyment, pain and sorrow are clear to see – but this goes to show that exactly what it is animals feel and the quality of their being bothered by their situation is a matter neither philosophy nor science has as yet managed to settle.
If we strip away the factors that muddy the issue of domestication - cases of neglect, the way animals are removed from the wild, problems within breeding - we're left with the core question of whether animals can live as full a life in our homes as they would in the wild. Would dogs not be better off having the run of an entire forest and chasing prey than they are getting to stretch their legs when we can be bothered to take them out and feeding from a bowl?
Maybe the answer is no, but their subordination and any corresponding negative effects are worth it for the joy they bring us? I love dogs, I love their loyalty and affection (or at least what we perceive as loyalty and affection), I like their propensity to jump around like a maniac and I'm fond of their intelligence and their utter stupidity, but am I putting my enjoyment for having a furry companion above their well-being? We might be well beyond that now, with dogs being domesticated centuries ago, but I need to be able to look him in the eye, damn it!
PETA has criticised the way fish are treated as "mere merchandise", as "decorative ornaments" which "few people realize just how much they suffer", the aquariums for which can never match up to an open ocean.
The organisation told me it does not oppose "kind people sharing their lives and homes with domestic animal companions" (though at press time there was no definitive list of exactly which animals that does and does not include), but that it finds it "amazing that there are still people who think crocodiles, snakes, and other wild animals should be taken from their natural homes and put in some murky tank in a British back garden or confined to a small glass case like a trinket."
The mystery of exactly what it is animals think and feel may forever elude us, as might our certainty that keeping pets is a justifiable practice.