You know, Cloud, if you really want, you can see the difference for yourself. Take a betta who has been living in a 1gal container for a while and try putting him in something at least 3x5 times that size. And see if you really cannot tell that the fish is happier.
I'm no great "example" as a betta keeper. My betta at work now lives in a large bowl, which stays at the right temperature due to ambient temperature being very high, but does not have a filter. I make up for the lack of filter by being very consciencous about my water changes, so that ammonia is always next to 0.
Anyways - when I got my first betta 3 months ago, I had the same misconception as many newbie owners. I specifically got a betta because I bought into the lie that you can just keep them in a small container and so it was going be "perfect" for at work. I had seen somebody else have their betta in a 5 inch bowl and since I considered that cruel, I used a "generous" 3/4 gal bowl, which was like a ball cut in half, so there was more lateral room for him to swim. He had stones and a little plant, was being fed, had his water changed routinely and was in good health. He could have been swimming back and forth, but he hardly moved around and mostly just rested on his little plant.
I was trying to learn more about bettas and unfortunately at first got to all the wrong places. I even read on one website where somebody claimed that he had a betta in a large community tank and that his betta did not swim around at all, but just kind of hung out in one corner - LOL. Anyways, so I thought I was doing "fine". I wanted to find out how often exactly I needed to change the water and could not find any exact answer, except that somebody on a forum said to test the water daily for ammonia until it shows and then change the water always a day earlier.
I got an ammonia testing kit and soon found out that with this small of a container I would have needed to do a water change every 24-48 hours in order to be able to maintain the "quality" of the water. Since my fish is at work and I can't really do "daily maintenance" I decided that I needed to get him into a container 3 times as large, so that I could reduce water changes to only once a week.
So I got this huge 3.5-4 gal bubble bowl. Originally I really just bought it out of "laziness" to cut down the amount of water changes I needed to do. And as soon as I put Azumo into his new large home he has been like a "new fish". I kept everything the same. The water, the temperature, the stones at the bottom, his plant, his food. I only added one more large ornament (fake tree trunk with a bunch of holes), since there was more room. And now he is swimming around all the time and NEVER rests on his plant he used to rest on. Everybody in my office instantly noticed the change and commented on the fact that he was so much more active now.
And having seen this with my very own eyes I am a firm believer in what everybody on this forum says. 3gal is the lowest TOLERABLE and generally people should not really consider anything below 5gal. My situation currently is that I am working two jobs and I am only home long enough to catch some sleep and get going again. So I actually am able to interact with by betta a lot more when he is at work than if I had him at home. I am doing everything I can to give him the best possible living conditions and I swore myself that if he does not get to live out the minimum of 2 years in this set up that I will not buy another betta to replace him. As I am definitely not into putting any animal through any kind of hardship. If I had know what I know now I would have never bought a betta. I fell in love with Azumo and it would break my heart to give him up now, so I am keeping him and making the best of it.
So the problem is really that the LFS need to make money. So Petco sells these "pretty" coral betta stands which hold a 4" diameter bowl as the betta "home" and the salesmen will happily tell you that this is a perfect home for a betta. I mean just looking at how many bettas they get in shows you that half of them must die right in the store and the majority of the other half are "replacements" for those bettas who died in people's "betta vases" etc. Many people on this forum buy bettas from their LFS just to save one of these beautiful creatures and that's why they feel so strongly about this.
Anyways this thread was really supposed to be a happy display of peoples fish and tanks and maybe we should start another thread if there is going to be a lot more back and forth on this. All I can say is SEEING IS BELIEVING. And rather than arguing about how you think the guys answering you are wrong, I suggest you actually try it and SEE for yourself. Only if a betta is kept in poor condition would you NOT see the marked difference of their disposition and activity level when keeping them in a 1 gal container versus a 3-5 gal container.