So those areas are or are not populated by extremely dangerous hillbillies?
They are not, no more than any region with a mildly insular culture is. In fact, the Applachian stereotype is one of the few highly negative stereotypes still allowed in American media because it's about a predominately white population. If it was about any other ethnic group it long ago would have been seen as what it is.
Bear in mind, the stereotype is founded on long conflicts between ethnic groups dating back to before the foundation of the United States. You see, the heartland of the Appalachian mountains, the Shenandoah Valley and the Applachian mountains of Virginia and West Virginia., were predominated settled by the Presbyterian Scots-Irish. Meanwhile they the Piedmont and Tidewater of Virginia was settled by the Anglican English.
So, there was a pre-existing serious divide there culturally dating back to colonial times. Take all the English negative stereotypes about the Irish (Scots-Irish means "Protestant Irish" effectively, but it's more complicated than that) and transplant them to how the English colonists of the region felt towards the Appalachians. Then add in the Slavery issue. You see, the Appalachian Scots-Irish were not really that big on the entire "slavery" system and you frequently saw routes of the underground railroad moving through their territory. Further, economically speaking the slave plantation system that dominated the South in the 18th and 19th centuries was not economical for the Appalachians, leading to those regions being economically disadvantaged (and thus politically disadvantaged) compared to the wealthy elite regions of the South... furthering division. And, of course, with such hostile divisions between them on major political, religious, and ethnic issues, the wealthy English descended elites, who controlled the media and academia of the South, tended to portray them as backwards subhumans.
Then came the Civil War. Remember: Virginia used to hold all the territory of what is now Virginia and W. Virginia, what West Virginia is was the counties of Virginia that refused to secede from the Union in the Civil War and while you also had many folks from the Appalachians fighting for the Confederacy, it was much more Unionist than anywhere else in the South.
But we're not done yet. In the post Civil War era you'd expect the Appalachian parts of the South to have been favored by the Federal government since they were a hotbed of Unionists through the war. But you'd be wrong. You see the Appalachian mountains are some of the oldest mountains in the world and at one time in deep ancient history they were on the sea bed right before a major die off. Which means that the Applachian mountains have some of the most significant and high quality coal deposits
in the world. Northern industrialists and the railroads absolutely, positively NEEDED that coal, and they would stop at nothing to get it as cheaply as possible. So they weaponized County, State, and even the Federal government against the folks of Appalachia to steal land, force them into employment in the mines in the worst kind of situation, and did everything they could to prevent them from unionizing (up to and including deploying the Pinkertons and US Army against them). In order to justify such oppressive measures the industrial elites and media of the time continued to subject the Applachian folks to highly negative portrayals in media.
This continues to this day, as the Appalachian culture is highly religious in protestant Christianity. It was highly influential in the Charismatic movement, the Fundamentalist, and to this day it is Appalachia that is the home of many of the Conservative Christian strongholds, for instance, Falwell's Liberty University is situated in an Appalachian city. They also are one of the strongest proponents of expansive gun rights in the US and, due to the aforementioned long history of negative involvement of State and Federal government, tend to be highly skeptical of government intervention into things (and I haven't even touched on things like Prohibition and how that negatively impacted Appalachia).
This means that almost all Appalachian values are at odds with the values of the urban elites, and as such, they are consistently demonized in media.