Benevolence

A highly advanced alien race arrives unannounced offering to help us make our world a better, safer place. With unbelievable technology far beyond human understanding, they seem able to ignore all known laws of space, time, and physics.
They deny all those natural laws that we find undeniable. They have the most profound knowledge of Earth's past as if they have experienced it. They know the most minor details of our lives. They seem to know our thoughts and our personal motivations. They promise to bring peace and eliminate needs. They promise no one will ever be harmed by their presence, and they promise they will take nothing but memories. Most importantly, they promise freedom.
But there is a catch...