Well i can't find the article right now. I know whats an argument with no proof right? The best i could find for right now is reviews from people who have kept them.
Read the reviews at the bottom of this page How to keep your Betta splendens with pictures
. And I want to point out that im not saying bettas can't ever be kept in large populated community tanks, it's just that i've read they often fare better in a sparsely stocked tank or on thier own.