Not true, there was a very successful COIN operation in 1965 in the Dominican Republic. It involved the 82nd Airborne and the 6th MEU. Not much has been written about this because it was handled rather quickly compared to most COIN ops. But there are definitely some lessons learned that we have forgotten, one in particular was the extensive use of PSYOp's.
Here is a link for the 82nd version of what happened. Short article but it is revealing. Anyone else on this site that knows anything about this or where more information is I would appreciate knowing about it.

http://www.bragg.army.mil/history/Hi.../PowerPack.htm