On reflection, I think the zoo arguments more or less balance out. The Pi view that animals are safe and protected versus the alternative view that zoos are inherently bad. So spacious well-managed zoos might be ok in principle, but they will still be stressful for the inmates due to the unvalidated visitors - they cause the taunting, provocation and general pushing at territorial boundaries that disrupt any peaceful existence.
But even for the best zoos I'd still draw the line before whales and other sentient beings. They should be free and exempt from zoological restriction.
Yet we still encourage the confinement of apes in small enclosures, taunt them, provoke them, laugh at them, deprive them of normal social contacts, restrict their exercise, give them artificial diets and generally create the complete antithesis of the natural environment in which they are evolved to thrive.
Of course I refer to The Human Zoo. Thank you Desmond Morris.