We're on a thread nobody is reading, but obviously I don't think your argument is winnable. Goldwater lost, but Nixon won, on explicitly the same racial strategy. Nor is the chronology of the ideological sort really disputable.

Goldwater's civil rights stance defines the modern Republican party. The party has moderated since Goldwater, of course, but Goldwater's positioning literally restructured US politics, from a de facto 4-party state (in the 1970s, Republican support for abortion rights was still an open question! There's a 1970s-era GOP platform where debate on abortion is a plank!) to the 2-party "liberal/conservative" one we have today. Rockefeller wouldn't even be a Kiwanis Republican today; he'd simply be a Democrat. Phil Gramm did become a Republican; in fact, almost every party switcher in the US after the Civil Rights act switched to the GOP, because they were fleeing the Democratic party after the Civil Rights Act.

The idea that the modern Democratic party is somehow accountable to votes against civil rights legislation is D'Souza-ism. It ignores the plain fact that those Democrats became Republicans, and, to a lesser extent, a bunch of liberal Republicans became Democrats. You see it clearly in the candidates themselves, but also even more clearly in shifts among voters.