Now, director Daisy Asquith has spoken out to condemn messages her team has received from many of the band's online devotees.
"Their response to the film is so much more extreme than anything I chose to include," she said.
"It's really been quite shocking. I think the response itself is proof that we didn't just pick the most extreme fans there are.
"Channel 4 have had threats and masses of hate directed at them. I've also had masses of hate directed at me."
Channel 4 said in a statement the documentary followed a number of fans who, "by their own admission, are obsessive about the band".
"Whilst not suggesting that the girls featured represent all 1D fans, it examined the impact social media has had on teenage fandom and how it has developed a new form of idol worship for many teenage girls.
"Both Channel 4 and the filmmakers took the utmost care to produce a documentary with genuine affection and respect for the fans."
- WENN