Buffy the Vampire Slayer 3x11

Gingerbread

Picking the wrong night for mother-daughter bonding, Joyce discovers the bodies of two children apparently sacrificed in an occult ritual and she rallies the adults of Sunnydale convincing them to rid the town of evil, including Buffy, Willow and Amy. Giles soon realises that the children are actually demons that do not kill people themselves but invoke fear and panic and gain their power by watching normally calm and sane people persecute each other.