well, I can see where both of you are coming from.
they actually don't originate from streams, but from rice patties in siam, a very low flow area. to much flow can frustrate bettas, but their are ways of moding them to allow for JUMBO filtration, but littleflow. Now one thing ya'll may want to consider is that in the wild they live in some pretty nasty water, but in the wild they also don't live long. So maybe cleaner water than in nature is better maybe not. But one thing is that they definantly do need some kinda heat, not necessarily in the water, but definantly to keep the air moist and warm, best achieved simply by having a hood and a heater. a lack of this kinda air will hender the labrynth's ability to operate. Now that coupled with a lack of a filter, is very bad. See a betta will either get oxygen from the water or from the air. Either way, the CO2 is gonna go into the water, now this is fine in a tank with proper surface and water movement, which allows gas exchanges, preventing a build up of, for a lack of a better term, "bad gases". Now if you do not have any movement in the water then it follows accordingly that their will be a serious 'bad gas" buildup in the tank. Now with no way of recieving oxygen from the tank, the betta must go to the air. Now if the air is too cold and dry, then as said before, henders the labrynth's ability to do what it does, thus stressing the fish out, and in very serious cases "suffocate" to death.
HTH