The rural purge was inevitable as long as advertisers dominated television broadcasting. When CBS started skewing older again in the '80s with shows like
Dallas and
Murder, She Wrote, their bottom line suffered as advertisers, recognizing that CBS' large viewer base was concentrated in demographics that didn't spend a lot of money, started turning away from them. It's also why The WB was so successful in the '90s, and why The CW and ABC Family are so successful today -- their ratings are tiny compared to the big networks, but they're overwhelmingly concentrated in the lucrative teenage/young adult demographic, and advertisers love them for it.
IMO, the only thing that could really prevent the rural purge from fully sweeping the American TV landscape would be to have a successful public or non-profit broadcaster in the US, one that doesn't depend on advertising and is instead focused on serving the widest swath of the American public rather than the most lucrative demographics.
NET, a non-profit educational broadcaster in the '50s and '60s, would be a great source of butterflies for this, especially given their shift in the '60s towards more entertainment and current affairs programming with mass appeal (such as
Mister Rogers' Neighborhood). It had a big problem, however, in the form of their news/documentary program
NET Journal. It was acclaimed as one of the best such programs on television, especially after CBS' news department was gutted by pressure from advertisers, but it also infuriated conservatives (especially their affiliates in the South) with its damning reports on racism and poverty. One of those conservatives was Richard Nixon, and you can bet that that figured into the government's management of what became PBS. Furthermore, NET was always dependent on grants from the Ford Foundation, and by the late '60s, they'd invested $130 million into the network with little to show for it. When they cut their funding, this forced affiliates to turn to the government for assistance, leading to the creation of the Corporation for Public Broadcasting in 1967 and later PBS in 1970.
Ironically, "dumbing down" NET may well be the only way to save it and prevent the conservative movement of the '70s from destroying it once it becomes federally-funded. That, or find a way to get it self-sustaining in the '60s while keeping it non-profit, without having to turn to government funding in the first place. (Maybe it scores a hit program or two, or an episode of
NET Journal makes a particularly big splash and resonates with a large section of the populace, leading to universities, charitable foundations, and cultural associations providing investment?) That way, you'd have a successful fourth network that isn't under pressure from advertisers to cancel everything with a tree, as Pat Buttram from
Green Acres described the rural purge. I find it ironic how the conservatives of the time, by essentially declaring war on public broadcasting, enabled the domination of television by the very same "coastal elites" that they railed against.