I want you to imagine a society almost identical to your own today, except everyone is said to be completely virtuous.
It is definitely shocking for people of your world to witness such magnitude of virtue, or I shall say, the suppression and obscuration of all treachery, greed, and jealousy. This narrative appeared so convincing that I used to believe it as well.
I know you have questions. Does this mean this world have no crime? Are there still police and soldiers? Does the government hand out money to everyone? To answer all your questions I'd have to write an encyclopedia. I'd rather you secure the answers yourself.
The Pacifica Academy is the most paramount education institution in our world, where future leaders are forged. It is similar to those upper class boarding schools in your society, but even more grandiose. Pacifica is secluded on a mountain, big enough to be a small town, and packed with enough alimentation and infrastructure to survive a nuclear winter.
Pacifica's character education is the most successful in the new world, making its students seemingly morally flawless. Internally, in lieu of drama, bullying, and peer pressure, Pacifica students all claim to love each other. Externally, Pacifica students display their magnanimity through countless acts of community service, and each time they would shed their heartfelt tears — oh how mature and empathetic — while witnessing the cruelty of human condition.
Perhaps it is this purity that made Pacifica their target. None of us know why they attacked Pacifica. None of us know how they infiltrated the well-secured academy. We don't even know how anyone could have the mind to do something so morally despicable. However, the attack was the most innocent episode, comparing to what was to happen next.