The following is a history of how the word "coonass" became associated with Cajuns, and of how Cajuns are a federally-protected national minority. 

From my experience, Cajuns will differ on whether the term is offensive. I know most of the older generation do find it offensive, and it is probably because they are familiar with the origin. I, as with most people regarding offensive words, feel that it depends on who is saying it and the context of its use. Basically, if you call me a coonass, you'd better be a close friend. 

"Coonass" is an increasingly controversial term in Cajun Louisiana (i.e., the 22- parish Acadiana region). 

In July 1980, Cajuns were officially declared a federally-protected national minority per the case "Roach vs. Dresser Industries." Historian Carl A. Brasseaux writes in "The Founding of New Acadia: The Beginnings of Acadian Life in Louisiana, 1765-1803" (Baton Rouge: LSU Press, 1987): 

"The plaintiff, Calvin J. Roach, who claimed Acadian descent through his maternal line, allegedly was fired by an oil-field service business when he objected to his Texan supervisor's repeated use of the pejorative term "coonass" in referring to Louisiana Cajuns. Roach consequently filed suit against his former employer for discrimination, banned by the Equal Employment Opportunity Act. Despite the defendant's argument that Acadia had never been an independent country and thus was incapable of producing a national minority, Judge Edwin F. Hunter ruled on July 17, 1980, that Louisiana's Acadians are of "foreign descent" and thus entitled to the full protection of the aforementioned federal legislation." 

In "Louisiana Law Review" (46-July 1986), attorney James Domengeaux traces the terms etymology: 

"In WWII, when American troops were stationed in France, it was necessary that the forces establish and maintain communication with the Free French Forces inhabitants. Naturally, the French-speaking Louisiana soldiers provided an invaluable resource. The French soldier, possibly threatened by his "long lost cousin," referred to the French-speaking American soldiers as "conasse." The French noun "conasse" is defined as a "stupid man or woman; used specifically for a bungling prostitute; to a prostitute without a health card; a man who does stupid things; grossly stupid person." The French word "conasse" phonetically resembles the American slur "coonass." The non-French speaking soldier, either out of jealousy or invidious jest, began to harass the Louisiana soldier by calling him "coonass" as a take of the word "conasse" used by the French forces. After WWII, large numbers of non-Louisianans came to South Louisiana for economic reasons and imported the use of the slur in referring to the Acadian inhabitants. Unfortunately, a small contingent of the Acadian population welcomed and promoted its use. This ignorant acceptance was done with the unfortunate belief by some that the term is "cute" or "humorous." Be that as it may, the majority of the Acadian people despise the slur's use. The slur does not have a proud genesis, nor is it indicative of a proud people." 

Resolution: the Louisiana Legislature condemned the use of the term "coonass." The legislative body traced the slur's infamous history and condemned the sale of any items containing the word. And, if I'm not mistaken, it's illegal to use the term "coonass" on radio and television in Louisiana.