While I never took offense at being called a honky, a hick, or a redneck, I don't buy it not being a derogatory slur in some context. Perhaps distinguishing more between class than race, but still derogatory.
Your argument is akin to saying "n*****" is no longer a racial slur because black people use it to refer to each other all the time, and even take pride in it. You and I both know the "n-word" is still completely unacceptable in most contexts. It shouldn't be surprising that honky, or hick, or some other stereotypical term describing or implying those of us with rural backgrounds as backwards, ignorant, and generally impoverished could be similarly taken offense to, as well. Again, I usually don't care, but I could see how some could.