I have a coworker who thinks keeping fish in aquaria is cruel - what's your opinion?

Personally, I don’t feel that fish have adequate cognitive ability to chafe at the confines of a tank. If the size is adequate, the conditions appropriate, and the care knowledgeable, I don’t have a problem with it (although I always want to rescue all of the poor bettas in their tiny cups), but she’s appalled at the thought of keeping fish in a tank. I had never even considered the situation from that point of view. Have you? What’s your opinion? (Assuming that we’re talking of appropriate species – no fast swimming, free ranging species that cover great territories like tuna or salmon.)