A handshake is a social construct. So is a $20 bill, Mass, democracy, and disco dancing. Social constructs are fascinating because they are made real only by agreement. Should everyone - or even just most people - suddenly agree that handshakes are dumb, currency is not to be trusted, Mass is in error and democracy or disco are out of fashion ... well, theses suddenly become ideas instead of realities.
This is not to say that social constructs are arbitrary - any more than car design is arbitrary. Some designs move better on the road and others move better off the showroom. Design is essential to success in a car. Even though in theory car designers have a large number of options to choose from, in fact they are constrained by variables like fashion, the laws of physics, and the price of gas.
The dynamics of social constructs are fascinating. Collectively, our understanding of them is at best sketchy. Few individuals understand the concept; even fewer know how to operationalize it. Yet there is perhaps no area of inquiry that is more important to explore or to understand, no domain the mastery of which would do more to promote progress.
Which is to say that we should be funding research into this area of inquiry. Attempting nation-building in Iraq without research into social constructs to draw from is like trying to build a plane without developing some theories about avionics and as much as anything reveals our ignorance about our ignorance on this important topic.