In the last 24 hours there have been open letters flying all over the place. After Miley Cyrus mentioned Sinead O’Connor in a Rolling Stone interview, the Irish singer wrote a manifesto warning the American pop idol not to be exploited by the music business. “Please, in future, say no when you are asked to prostitute yourself,” she advised on her website. Cue charges of slut-shaming and misguided sexism. Amanda Palmer has weighed in on her blog, telling O’ Connor to back off. “Who says Miley can’t flip the script anytime she wants?” she asks.

Talking to Rolling Stone, Cyrus said that her notorious ‘Wrecking Ball’ video in which she snogs a sledgehammer and writhes around naked was inspired by O’Connor’s 1990 video for ‘Nothing Compares 2 U.’ O’Connor makes the interesting point in her letter that when she made her debut album ‘The Lion and The Cobra’ at 20, the age Cyrus is now, she wore her head shaved, androgynous clothing and choose not to be sexualised. “The look I chose, I chose on purpose at a time when my record company were encouraging me to do what you have done. I felt I would rather be judged on my talent and not my looks,” she explains. There’s is no doubt her choice to flaunt her intelligence and talent instead of her body influenced and encouraged many singers that followed to do the same.

But whether O’Connor should’ve doled out advice or not, Cyrus’s response to the letter was deplorable. Writing on Twitter, Cyrus compared O’Connor – who has openly battled with mental health issues – to the actress Amanda Bynes, who was hospitalised after a mental breakdown earlier this year. “Before Amanda Bynes…. There was…” she posts before an image of Tweets sent previously by O’Connor asking for psychiatric help.

By implication, Cyrus is saying that because O’Connor has had mental health problems she is not in a position to comment or hold an opinion. Would she say the same if O’Connor suffered from a broken leg, or cancer? Mocking mental health in this way exacerbates stereotypes that depression – and specifically in O’Connor’s case bipolar depression – makes a person less-than and a social pariah. Cyrus has 14million Twitter followers, a quarter of whom will probably experience mental health problems at some point in their lives. There is no bigger pop star in the world than her right now; after the VMAs debacle she has trended on Twitter almost every day. Her influence is considerable. Let’s hope her comments won’t have forced closed any mouths of people who need to get help.

The charity Time To Change, a programme working against discrimination faced by people who experience mental health problems, have called for an apology. As they say, stigma and discrimination ruin lives. Cyrus should do the right thing, though I fear the damage has already been done. It’s shocking and sad that someone in 2013 holds such a backwards view.