People who have had a traumatic childhood usually develop a mental defence which protects them emotionally from these traumas. This act of defence can be continued into later life even when it is not needed and this is why some people can react badly to being in romantic relationships.
"People maintain the defensive posture that they formed early in life."
According to Dr. Firestone, childhood experiences can deeply affect how an individual thinks of love, relationships and attachment in later years.
This is not always obvious, as people engage in these behaviours in an unconscious way. However, it seems like people who experience negligence, abuse, or isolation during childhood have a tendency to engage in unhealthy and unloving relationships. They tend to be individualistic, afraid of commitment, reluctant to open up or fearful of being vulnerable, all very important characteristics of romantic relationships. On the other hand, people who had healthy childhoods tend to be better equipped to engage in this type of relationships successfully.
In essence, the author is stating that the degree of diversity that exists in the United States is much greater than any other country in the world. Any time there is a lot of diversity, there is the potential for problems.
