You are correct about “rednecks.” The term began to mutate in the early 1900s when socialist “progressives” who were pushing a form of “social justice” Christianity without God mocked those who believed in the Bible as ignorant, backwards “rednecks.” The battle culminated in the Left’s takeover in the early 1900s of the Presbyterian Church and the purge from Princeton seminary of Christian professors.
The purged professors had been advocating that socialist views had to be rejected and that the Church had to return to the “fundamentals” as set forth in the Bible. Those purged from the Presbyterian church by the Socialists were also disparagingly called “fundamentalists,” so that is where that term came from as one being used to denigrate Christians.
The descendants of those leftists pretty much gained complete control of all the mainline denominations by the 1950s and 1960s, and you can see the results today.
I have another term for “blasted” at least as applies to the PCUSA!