In the caption for the photo, taken during the 2003 MTV Video Music Awards, she wrote: "Gay or straight, no hate. Stop hate. Stop violence."
She also posted another image from a speech she once made where she said: "You cannot use the name of God, or religion, to justify acts of violence, to hurt, to hate, to discriminate."
The "Vogue" singer also posted a third photo of her face with the caption: "You cannot use religion to treat people badly. You cannot use God’s name to treat other people badly. We all deserve love.”
Backlash on Twitter was swift and brash.
"Are you serious right now? This isn't about you and your fake kiss for publicity," wrote one fan.
Another Twitter user replied: "Really? 50 people died and you want to make this about you?!"
On Instagram, a fan posted: “That's just two straight women generating publicity for themselves in a way designed to titillate straight men, nothing to do with the LGBT community.”
Since the backlash, Madonna posted a collage of the victims, captioned: “You Will Not Be Forgotten.”