I would not go so far as to say everything we have been taught - every influence - from other humans, is the foreign installation. Certainly it is a question as to what a human would look like without any human influence, but I don't think we would like the result, because a huge part of us is gregarious. Taking that out would be taking out a huge chunk of our natural essence.
Distinguishing which influence is installed to our detriment by a predator on the human species, and which is a healthy influence instilled into us by our human relationships, is what spiritual development is all about. There is no easy answer - it has to be seen from the viewpoint of learned growth through insight. Once we have grasped that so much of existence is about optics, then we can pick which optic leads to our preferred goal.