People always have anecdotes about how happily they've kept fish in small volumes of water - people who kept guppies in large pickle jars, for example.
If you know what you're doing, you can certainly keep a betta well in a small volume of water. Plants are a must unless you are using a rather sterile setup (like you would do for breeding)
Unfortunately, most people don't know to feed very little, change the water often, and keep the room a comfortable temperature. A betta really needs it warmer than 72-74 degrees, and this is considered by many to be room temperature.
Few people think to put actual aquatic plants in with their "bowl bettas" - lucky bamboo is probably the only commonly used plant.
While I agree with you that it is erroneous to compare two species (humans and bettas, dogs and bettas) this comparison is made for a lack of a better analogy. There is really nothing else like keeping a betta in a bowl - no comparison is going to be adequate.
However I feel certain that a betta would be more comfortable if it were kept at a stable temperature and given some filtration, a sponge filter or the gentle (rather puny) filtration of a built in small aquarium kit. I've had bettas do fine in quiet community setups with normal filters going, as long as they don't roil the water too much, they do fine - especially female bettas.
Bettas are not very different from sparkling gouramis, or honey gouramis, or paradisefish, and no one would suggest putting them in a bowl - even though they also have a labyrinth organ. I object to the whole "bettas like stagnant water" theory because inevitably, there is going to be some intermittent pollution in between when their food gets digested (or their uneaten food, no matter how trivial an amount, begins spoiling) and when water gets changed. Sure, plants can process it...
But the aquarium in question (what this thread is actually about) is not really conducive to keeping plants, it's obviously just meant for exactly what is presented. Some gravel, or marbles, and a fake decoration. I doubt the light can grow any plants - it must be LED, if it is running on so little power!
I have kept bettas in half gallon bowls that looked extremely happy, active, colorful and content.
To say that keeping a betta in a smaller body of water is the same as making a human live in a closet is an argument that simply does not make any sense. You're comparing the needs of medium sized terrestrial mammals with enormous brains to the needs of tiny aquatic fish with brains the size of a food pellet.
Comparing the life of one species (betta splendens) with that of another (home sapiens) is illogical. We are entirely different creatures both physically and mentally. Bettas are fish who have evolved over millions of years to live in very small, often stagnant pools of water with very little oxygen. They can breathe both air and water. Humans are mammals who evolved over millions of years to walk, run, jump and travel in wide open spaces while breathing only air. We are simply not equipped to live in tiny sealed spaces.
There is a reason why bettas don't do as well in as other fish in currents - they aren't adapted to the conditions of voluminous, volatile waters. Just the same as how other fish couldn't survive in a betta's habitat as they have no labyrinth organ.
