Let's review the sorts of pop culture examples that lead to the perception of being a racist, sexist, and generally bigoted person as being synonymous with being a redneck.
In the closing scene of Easy Rider, Peter Fonda and Dennis Hopper are riding their motorcycles out of New Orleans and a truck comes up behind them. Pickup truck--redneck mark #1. One of them says to the other, "pass him, let's give him a scare." Accent--redneck mark #2. You will note that they are probably socially conservative (like the vast majority of rednecks are) based on their antagonism towards Hopper, as well as their close haircuts and the demographic makeup of the region they come from. The man riding shotgun then pulls out an actual shotgun, points it at Hopper, and shouts derogatory remarks at him. Hopper flips him off, and the redneck shoots. Please note the use of stereotypical redneck traits immediately surrounding a man who shows himself to be a murderous bigot. Thus, a Pavlovian association is formed between redneck and bigot in the viewer's mind, even when someone the judge to be a "redneck" displays no bigoted behavior. Fonda stops to check on Hopper, then rides in the direction they and the truck were going, to go get help. By this time, the shooter has convinced the driver of the truck to turn around and check on Hopper. We are unsure whether this is out of human concern, or to make sure he's dead. The truck passes Fonda going the other way now, back towards Hopper, and the trigger man pulls the shotgun again as Fonda draws near, and the shot hits the tank on his motorcycle, causing a large fireball and blowing him to Kingdom Come. As the truck drives away and credits roll, one can hear the two men laughing.
Given the tendency for rednecks to grow up in the South, and the the American South's history as a racist, sometimes sexist, generally intolerant cultural area, it is not statistically suprising that many rednecks are a little right-of-center on the mainstream political spectrum. Rednecks tend more than the general U.S. population to be
- somewhat racially biased (many without even knowing it-- heck, everyone is, just some more so than others)
- wary & unaccepting of outsiders (remember, small-community upbringing is a common formative factor for rednecks, even if that is just a neighborhood or trailer park within a big city)
- more outspokenly critical of anyone whom they have concluded to not be straight, especially men. This escalates to violence much faster among rednecks than among, say, your average New Englander.
However, I believe that since prevalence of these stereotypical (and accurate) redneck traits drops as cultural setting changes, it is the setting causing both these bigoted behaviors and redneck-ism, not redneck-ism causing the behaviors.
I hope that's a satisfactory answer, ma'am.