I agree that they should not be kept the way they normally are. But it can be a slippery slope when you go down the cruelty to fish road. When is any fish kept in an aquarium properly housed? We can set any cut off line for the appropriate number of gallons and tank footprint for any given fish but most of us will never come close to giving them the kind of space they would have in nature. I can argue that most of my fish live longer in my tanks than in nature so I am actually doing them a service. But most of them will never reproduce so I have deprived them of their most basic reason for being alive. I have been keeping fish for a long time and will not likely give it up but if you follow the Betta in a cup thinking far enough most of us just have a slightly bigger cup and should give up keeping fish.
Ok I do get your point, but there is a huge difference between the way we keep our aquarium fish and the way bettas are kept in cups. We supply our fish with fresh water each week, we provide filtration , we provide food and we try to approximate their natural environment, albeit in a small way, but we do not torture them. At least I don't think my fish are being tortured. The little bettas in cups have no food , no filtration, not much air, and an environment that is like nothing they would live in naturally. Their water is polluted with their own waste. They have no hope unless someone comes along and buys them. Yes, buying them does keep the process going I admit. I don't knpw what the answer is, do you?