it was a horticulture training facility in the middle of the capital city of Atlantis
their policy was non-interference, and did not go out conquering and enslaving the rest of the human race, just being friends and sometimes giving warnings about disasters their astro/geophysicists were predicting
a group of them wanted to go out and turn humans into slaves, and there was a big war, and then they ran away and started enslaving the people of the middle east, and spread out across the planet building pyramids everywhere and demanding human sacrifice and especially killing babies, ceremonial whoring, and other much worse things than even these