Well since I was talking to Linda Olson (IBC judge and transhipper for Thai breeders) we got onto the topic of isolation in bettas. She knew one breeder who kept cards between all his jars of males. She then continued to tell me about various experiments conducted with other animals. She then told me about a male who had been separated in total isolation for a long time. She then placed him in a tank of betta fry. He ended up being frightened of the fry for the longest time because there were so many of them and he couldn't hide anywhere without seeing fry. Eventually he grew out of it, slowly. Many people claim that flaring is stressful on bettas. Personally I feel it helps them stay healthy. Also all animals need interaction. Bettas interact by displaying their fins, spreading their gills and wagging their bodies. Another example is betta juveniles. If bettas are jarred and kept seperate from their brothers and sisters they may become depressed. Yes it does happen. As long as they're not in the same tank flaring is 100% OK.
Just thought I'd post my views on the topic.