They said that this change could help them to fight harmful behaviour. Otherwise it would not be able to fully control under its existing rules.
The Facebook policy of “coordinated inauthentic behaviour”, helps in dealing with the harms that are generated from networks of fake accounts. While the new policy of "coordinated social harm" will give the company a new authority to address harmful actions from legitimate accounts.
Nathaniel Gleicher, the head of security policy said that the policy is necessary because some people are increasingly trying to “blur the lines” between authentic and inauthentic behaviour.
He said, "We are seeing groups that pose a risk of significant social harm, that also engage in violations on our platform, but don’t necessarily rise to the level for either of those where we’d enforce against for inauthenticity under CIB (coordinated inauthentic behaviour) or under our dangerous organisations policy. So this protocol is designed to capture these groups that are sort of in-between spaces.”
He also mentioned that these new protocols could help Facebook address networks of accounts spreading anti-vaccine misinformation or people trying to organize political violence through their platform.