Here's another answer of mine from a question posed in the same book: Why We Should Love Black Women by Hasani Pettiford:
I speak from personal experience as a victim and a perpetrator, and in general.
Women hate on other women because of their own insecurities. Pure an simple.
Women see what other women have, which is oftentimes synonymous with what the hater DOESN'T have, and they covet it: men, money, materials, brains, body, confidence, peace, etc...
They try to figure out why they can't reach the same level: Maybe I'm not cute enough, skilled enough, too broke, dumb, fat, got too much negativity going on...
And to keep all of the blame from being on themselves (and because it's MUCH easier to blame your woes on others rather than take personal responsibility), you think of ulterior motives as to why she REALLY has all those things...:
She must be a hoe, she must be screwing her way to the top, she must have men giving her things/ rich parents, she must have gotten plastic surgery, she think she's all that...
In placing those negative attributes on the other women, it makes us feel better about our condition, because it says to us that we COULD attain those things if we wanted to, and that those women are no better than us. It's not about who's better or worse; it's about who wants it more. Even those who have gotten certain perks in their lives through means other than honest gain have a chance of losing it all because of the maintenance behind it, skills they haven't learned due to things being handed. It all depends on what's left when the surface is stripped; that's what will carry on.
Instead of congratulating those women who are on the up and up (because let's be honest, there are some women who aren't far from the negatives) we put them down and underestimate them because we aren't where they are. It's been a long time since I've had this mind set, and I now give credit where it's due, because it's hard enough as it is to make it out here, and we don't need negative energy from those who are supposed to understand and love us. I also try to uplift those who feel as if they can't be more than what they are. It all starts within the person.