Why are people from Louisiana called coon asses?

Not all of them are.

It is directed towards a Cajun. Cajuns came from Canada, they are originally from Acadia in the south east of that country. The British drove them from their homes in the time period of 1760-1790. They settled in Louisiana.

Some people say the French gave them the nickname but it's been proven the ethnic slur was around longer than they think.

Either the fact they ate raccoons or the fact they were thought to be below a black man in that time period led to the term. Because black people were called coons then by those who wanted to think they were the same as base animals. To be called that name meant they were thought even less of.

A lot of people get upset when they are called that. There are many reasons why. Either because people don't know the history of the Cajuns and think it's a cute nickname, or they really feel that Cajuns are what they are calling them. Both are wrong on many levels. The same as calling a black person ugly names. It's not right.

Thankfully most Cajuns will correct anyone who chooses to use it.

Coon ass is a term for a black person in the South. They don't seem to like it too much when you call them that though.

Coonass, or Coon-ass, is an epithet used in reference to a person of Cajun ethnicity.

Although some Cajuns use the word in regard to themselves, other Cajuns view the term as an ethnic slur against the Cajun people, especially when used by non-Cajuns. Socioeconomic factors appear to influence how Cajuns are likely to view the term: working-class Cajuns tend to regard the word "coonass" as a badge of ethnic pride; whereas middle- and upper-class Cajuns are more likely to regard the term as insulting or degrading, even when used by fellow Cajuns in reference to themselves.

Despite an effort by Cajun activists to stamp out the term, it can be found on T-shirts, hats, and bumperstickers throughout Acadiana, the 22-parish Cajun homeland in south Louisiana.

The origins of "coonass" are obscure, and Cajuns have put forth several folk etymologies in an effort to explain the word's origin. Some believe that the word refers to the Cajuns' occasional habit of eating raccoons, or from the use of coonskin caps by the Cajuns' ancestors while fighting in the Battle of New Orleans or in the Revolutionary War under Spanish colonial Governor Bernardo de Gálvez. Others attribute the term to the racial slur "coon," used in reference to African-Americans — thus implying that Cajuns are lower than African-Americans in social standing. Yet others hold that the term derives from the shape of Cajun women after having children (like a raccoon viewed from above). To most people, "coonass" is more or less synonymous with "redneck cajun".

The most popular folk etymology, however, stems from late Louisiana congressman and cultural activist James "Jimmy" Domengeaux, who maintained that "coonass" derived from the continental French word "connasse," which he contended meant "stupid person" or "a prostitute without health papers" (dirty prostitute).
(More at...)

http://en.wikipedia.org/wiki/Coonass

(noun) Vulgar, Disparaging, and Offensive. (chiefly in Louisiana and Southeast Texas) a Cajun.

[Origin: ‡ 1960–65; prob. alter., by folk etym., of LaF, F conasse - a contemptuous term for a woman, lit., vulva, equiv. to con vulva (< L cunnus) + -asse pejorative n. suffix]

http://dictionary.reference.com/search?q=coonass&r=66