I always end up defending academic research in management when I talk to a number of my friends with an engineering background. These are some of my thoughts based on explanations that I have given them. I could have asked them to read "History of Sociology", but chose not to, because that would have only strengthened their opinion. I try to explain it in my own words. Often, I have succeeded, but, I have also failed at times.
Inquiry into the whys of the natural world are needed to further our understanding of where we live and why we are the way we are. Similarly, inquiry into the whys of the other worlds that we have constructed as humans is also needed to lead a better life and be what we aspire to be. In the first realm are the natural sciences - physics, mathematics, biology, I hope you get the point. In the second realm are the social sciences - economics, sociology, arts etc. Marketing, as I see it is an offshoot of economics, but borrows heavily from disciplines such as psychology and sociology to understand the behavior of individuals and firms in the context of markets. As I progressed through my PhD I figured as a discipline Marketing had evolved to serve a certain purpose in the overall scheme of things and to address certain questions concerning "markets" that economics and other disciplines do not address. I am not sure if I will ever be able to figure out a good way of explaining to a naive listener as to what it is exactly that I research. However, I am sure I have a few models of explanation that I think are being effective :)!