There is no question that: 1) segregationists defected from the Dem party en masse circa the 1960s; 2) the defection was an immediate and direct reaction to Democratic actions on segregation on the national level; 3) the South flipped from D to R in the aftermath. The GP's one-liner is truer than your detailed rebuttal.

The South was solidly blue from the end of Reconstruction. A literal contiguous blue block in every single election from 1880-1948; sometimes the only blue states on the map. https://www.businessinsider.com/united-states-map-presidenti...

The defection was a messy period between 1948-1980. Following desegregation of the armed forces in 1948, the "States Rights Democratic Party" candidate for president carried 4 states against the Democrats and Republicans on a segregationist platform. In the next 10 elections Southern states defected several times from the mainline Democratic party candidates for segregation-friendly candidates -- sometimes to Republicans (Goldwater) but also to other third-party candidates (George Wallace, "American Independence Party") or to blue-dog Dems who weren't even running (eg Byrd).

By 1980 the South was solidly red; sometimes the only red states on the map. (At the national level. The transition was slower at state level and curious artifacts still remain today.)

To recap: Solid blue south from 1880-1948. Clear defection in 1848-1980. Solid red south from 1980-present. The defection was clearly led by segregationists leaving the Democratic party.

It's true that segregation lost support over time, and that Republicans drew lines to avoid becoming the party of segregation per se, and that other things were happening. In 1968 former Democrat George Wallace won the South with a brand-new third party, but he had had verbally moderated from "segregation now, segregation forever" in 1963 to leading his 1968 platform with "As this great nation searched vainly for leadership while beset by riots, minority group rebellions, domestic disorders..." [1] Wallace tried to run as Goldwater's Republican VP, but was rejected as too racist for the Republican party. Wallace's platform wasn't just race dog-whistles; it also listed student protests, war, taxes, etc.

Still, for the most part, the parent comment marshals technical truths to obscure the historical arc. It's true that segregationists wouldn't defect to the candidate that supports civil rights more; by 1980 this does not describe Republican candidates. It's true that most segregationists not change their local party affiliation; they did start voting against national Democratic candidates, and eventually for Republican candidates. Carter and Clinton are irrelevant to this historical arc.

By 1980, Republicans had lured white Southerners from the Democratic party (for president). They did so with a platform and candidates that reflected Southern racial attitudes, which were not segregationist by 1980. (The Democrats won the South with a segregationist platform from 1880-1948.) People can argue about the centrality of Republican appeals to the South across various axes, but there is a flawless historical record about the centrality of desegregation in ending the Democratic solid south, and it's not an accident that the Republicans are the modern party of "Total And Complete Shutdown Of Muslim [Immigration]" etc. Racial politics are a thing in the world, a thing in the US, and a thing in the D/R divide in every era.

[1] https://www.presidency.ucsb.edu/documents/american-independe...