Yeah, that's what I've heard about most sororities. There's not a lot of people that have long term successes. (I mean bettas usually live for several years, not just 2 or 3) A lot of times what I hear is that they work well in the beginning then eventually decline and die off after 2 or 3 years or less. I agree with russell that its more possible with a huge tank, I think its just the high stress environment. Sure, there could be that many female bettas that are near each other in the wild, but they have the option to get far away, which is an option a sorority doesn't give them. Plus, even if its only occasional nipping or chasing, a high stress environment can lead to a swifter death with any betta. *shrug*
So I'm on the side of not personally recommending it either. But, its up to you. As said before, some have had a relative amount of success.