After learning a lot about betta fish from this forum, I am shocked at all the misinformation out there. And this is not just personal recommendations from people who don't know much, there is also a problem among published books and other more official sources people who really want to learn go to.
This is from a book I have about tropical fish:
"Siamese fighting fish
about 3 inches (7 cm) long. As the name indicates, they are fighting fish- only the males, however- and are very aggressive with one another; consequently, keep only one male in your tank. Keep several females along with the male, because one lone female often will be hunted. Fighting fish are peaceable toward other inhabitants of the tank, however, unless they have similar fin veils. they do well in a community tank."
Stadelmann, Peter, and Lee Finley. Tropical Fish. Hauppauge, NY: Barron's, 2003. Print.
I don't know about you, but I don't think keeping a male constantly with several females is a good idea for Betta splendens.
(if you post misinformation you found, please do your best to properly cite it)