What's keeping humanity in Trek from exploiting other cultures is the fact that Earth and its colonies don't need
anything from a less advanced culture. Any resources that are needed are just as easily taken from empty worlds. In Avatar
, the Na'vi are sitting on top of some very valuable resources on a planet that is the closest to Earth but still takes immense resources to reach. In Trek, a starship would just pass on by to the next world possessing the resources sought, because warp drive makes it easy to find an empty world to mine.