The company did not release data on complaints, but it was a "huge volume", a product manager for site integrity, Travis Bright, said.
The online social network that has more than 800 million online users worldwide wants to put the brakes on conflicts and promote positive exchanges.
"We want you to have real friendships and build real community," Mr Bright said.
Facebook recently invited to its campus in Palo Alto, California, experts to share the science behind compassion and altruism. In the audience, engineers listened intently to ideas about humanising interactions.
Researchers from a Stanford University compassion institute and the University of California-Berkeley's Greater Good Science Centre said humans were hard-wired for compassionate behaviour and got physiological boosts from feel-good neurotransmitters such as oxytocin and dopamine when they deployed their better nature.
It was that science behind the benefits of good behaviour that caught the attention of Arturo Bejar, director of engineering at Facebook.
This year, Facebook piloted one project based in part on consultations with Stanford's Centre for Compassion and Altruism Research and Education.
After the talks, the company improved its "social reporting" tool to convey emotion, which helped connect people. Now, the tool let users click on a link to send a pre-written message saying, "Hey, I didn't like this photo. Please remove it."
With the new tool, Mr Bejar said 75% of those who posted an objectionable photo removed it.
"They feel more empowered and the friend becomes more mindful," he said. "Everyone learns from this."
Users could have sent a direct message to the person posting the offensive photo, but they rarely did, Mr Bejar said.
Struggling to find the right words was part of the reluctance, he said, and it was also a multi-step process.
Facebook's interest in a scientific approach to cordiality meant "a huge opportunity" to enhance social and emotional skills on a mass scale, which was especially needed among younger users, one expert at the event said.
"How many sixth-graders could name three emotions and strategies for regulating them?" asked Marc Brackett, deputy director of Yale University's health, emotion and behaviour laboratory.
"One," he said. "My son."
Dr Brackett has an idea for Facebook: for users younger than 18, build into their Facebook sites tips on developing emotional and social skills. One example is teaching children to take a deep breath before responding to a post, photos or other interaction on Facebook.
That is one facet of his lab's "Ruler" approach - recognising, understanding, labelling, expressing and regulating emotions - that Dr Brackett is discussing with Facebook.
"It's possible" such a design could become reality, Mr Bejar said, although he emphasised the company was only exploring ideas.
But a few pilot projects were likely to launch in the next month.
Dr Brackett said teaching younger pupils social and emotional management skills was needed urgently, as bullying and hurtful Facebook posts were distressing schools and disrupting academic performance.
Improving online social skills promised academic benefits too.
More than 200 studies show that pupils taught how to manage social interactions and emotions performed significantly better in school and in standardised tests than those without the training, according to the Yale lab.
Facebook knows it cannot engineer its way out of online friction.
"A lot of times the solution is not in the code, but in the interactions," Mr Bright said.
