Leyla Hussein, 32, said many were scared to speak out against FGM because they were worried about criticising another culture.
She decided to conduct an experiment to see “how crazy political correctness has become” but was left in tears by the end.
Approaching shoppers with the petition supporting FGM, she told them she wanted to protect her “culture, traditions and rights”.
In only 30 minutes 19 people signed it with some saying they believed FGM was wrong but because it was part of Ms Hussein’s culture they would add their names. Only one person refused to sign.
Her campaign against FGM is the subject of a Channel 4 documentary, The Cruel Cut, which features the shocking scenes where she asks people to sign the petition.
Speaking after the experiment in Northampton, Ms Hussein broke down and said she was scared by people’s reactions.
“I kept using the word ‘it’s just mutilation’. They were like ‘yes, you are right’. How can anyone think that’s okay?”
She added: “FGM is not culture, it is violence. Stop using the culture word. This is happening to children. We are human beings, we can’t watch children being cut, I don’t care what culture you belong to.”
Ms Hussein, who is co-founder of the anti-FGM charity Daughters of Eve, is calling on the Home Office to take responsibility for drawing up an action plan to eliminate FGM in this country.