A few notes...
F Troop was an ABC show, not CBS. It was canceled two years before the rural purge.
Gunsmoke remained on the air through the 1975 season. It’s demise had more to do with the show reaching the end of its run; it had been on the air for 20 years, and at the time, was the longest-running series in network history. BTW, Gunsmoke was saved from cancelation by CBS Chairman William S. Paley a decade earlier; Paley, the epitome of urban sophistication, intervened when then-network president James Aubrey announced plans to end the show. Aubrey didn’t last much longer at CBS.
Andy Griffith left the air at the end of the 1968 season. The show’s star and namesake wanted to take another shot at the movies (terrible career move); Griffith had planned to end the series in 1965; it took a new salary of $1 million a year to keep Andy on the show (and he was a majority owner of the program as well). That’s why Don Knotts left the show; all indicators suggested the program was coming to an end and Universal offered him a lucrative movie deal. Knotts took some of the show’s best writers with him, one reason “Griffith” declined in quality over its last three seasons.
In fairness to CBS, they were under heavy pressure from sponsors and advertising agencies to offer a new programming slate that had more appeal to younger (and supposedly more affluent) audiences in urban and suburban markets. Hence, the rural purge. Silverman was just following orders.
I agree with your central theme, however. Some of the shows that followed definitely coarsened the culture and helped push us into the cesspool of today. But some of the new shows, like Mary Tyler Moore and Bob Newhart, were instant classics, and better than the shows they replaced.
One final point: while some of the “edgy” shows like “All in the Family” were hailed at the time, they proved to have a very short shelf life. Both All in the Family and MTM did poorly in syndication; many of the local stations who spent heavily to re-run those shows regretted the decision and had to spend even more to find programming that people would watch. Meanwhile programs like “Andy Griffith” remain as popular as ever; audiences will be visiting Mayberry a century from now, while “All in the Family” will be little more than a TV footnote.
Demographics is destiny, and the fact is networks wanted to appeal to the folks who had more disposible income.
“Gunsmoke remained on the air through the 1975 season.”
My Dad died in 1976. My mother joked that besides his body just wearing out at age 79, the end of Gunsmoke was his last battle.
He loved the show and the first Maverick show. The Cartwright family/Bonanza was another favorite of his.