Because "redneck" is a term that is used to ascribe a set of characteristics to a specific group of people -- to stereotype them. And people who get called "redneck" would be reacting to a term that is meant to belittle or demean them my assigning negative or exaggerated characteristics to their ethnic group, and often to imply lower intelligence or ignorance.

So if someone objects to being called a "redneck," they can point to negative images, and OBVIOUSLY from this post, to a high degree of prejudice and bigotry exhibited towards them by people who would call them "rednecks."

NONE OF WHICH APPLIES TO THE USAGE OF THE TERM "A-RAB"!