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The 46-year-old controversial Irish singer-songwriter bluntly wrote:
"The music business doesn't give a sh- about you, or any of us. They will prostitute you for all you are worth, and cleverly make you think its what YOU wanted.. and when you end up in rehab as a result of being prostituted, 'they' will be sunning themselves on their yachts in Antigua, which they bought by selling your body and you will find yourself very alone..."
Cyrus responded by posting pretty crazy old tweets from O'Conner and comparing her to Amanda Bynes, who is currently on a psychiatric hold.
So what does famed feminist Gloria Steinem think of all this fighting and twerking and tweeting?
"I think they have different views of the world, and I would much rather be O'Connor," Steinem told Vulture at last night's Women's Media Awards. "I mean, she's a serious human being. Perhaps they both are, but we don't know that yet. But you have to remember that Sinead's background - she's been sexually abused. She was courageous in pointing out sexual abuse by the Catholic church. I'm sure it does pain her to see a young woman being oblivious to the endangerment of sexuality."
Steinem was also quick to note that she doesn't think the feud was a "catfight," but more "they're disagreeing on substance."
Vulture also spoke to actress Rosario Dawson on the topic, who had a bit more sympathy for Miley:
"For some reason, when men [express their sexuality], it's kind of like, cool, and masculine and mannish. But when these girls do it, it's like, 'You're too young.' And there's this responsibility that's put on them just because of being female, that they're supposed to be these role models. And I am interested in the idea that they're kind of flipping the bird to that and just going, 'I'm doing my thing.' I'm kind of trying to take in the information so I can be helpful, rather than just shooting from the hip and [having] knee-jerk reactions to their behavior. Because I don't know what it's like to be a young girl in America these days, you know what I mean? It's a different world. It's fascinating. And I kind of dig some of the ways these girls are twerkin' it."