Well...this is a controversy in the making
I'll agree that every fish deserves a cycled tank & believe it or not a 1 gallon tank can be cycled and maintained with no problems, with proper care of course. Using a turkey baster to "gravel vac" works great for weekly 25 -50 % water changes, without using a cheesy ug filter, or any filter
I personally house 20+ bettas,1 lives in a 10 gallon (because he's spoiled) 4 of which reside in 1 gallon tanks & they're very active & lively, the others have 2's & 2.5's , some shared (divided) and some flying solo, and each according to that particular bettas preferance. 1 gallon's suit some bettas perfectly, as a matter of fact I can think of 2 or 3 of mine that really have tooo much room in a 2 because they don't use the space since they're lazy bums & other's who parade all over their 2's with glee.
As far as heat goes...that's up to the caretaker of the fish to place them out of a draft and in someplace cozy and I believe that anybody who has enough concern for their fish to get them a nice house of their own would also be concerned about their fishes comfort. And in addition....anybody who's a member of a fish forum is also deeply concerned about gaining knowledge as how to care for their fish.You may have better results spreading your knowledge to the people in the chain stores who buy bettas and little bitty bowls, most of the people here know their bettas well & how to house them and tend to their needs
. The point being, each betta has different needs, and a loving home is 1000x better than a cold cup in a dept store wondering if you'll live long enough to see your next meal.