What’s killing the American middle class and why save it?

According to The middle class is shrinking just about everywhere in America, the middle class is shrinking because of the widening income gap and increase of the upper middle class. Major economic boost has help to build up metropolitan areas while at the same time destroying the middle class society that helped to build the US. If there is more of regulation on how these economic boost take place I believe it can help fix the widening gap of upper and lower class.