The "school" is really just a heat sink and reeducation camp for the goddesses and heroes. It redirects the energy and power of them at each other while also indoctrinating the heroes. It's why there's a caste system in the school so they fight with each other instead of the real world and regular people.
There's no such thing as a drug with no side effects. If not physical it's mental. They're going to get addicted to the power and since this goddess is the only supplier hmmm I wonder how they get more drugs. Komari is so frustratingly naive. She blindly wanders into danger, is saved by deus ex stupida, doesn't learn anything, repeat.