That's pretty much exactly what I'm going to say, mostly because the things you say are ignorant and uninformed. The party of lincoln pretty much abandoned 'racial equality' (if in fact, they ever really promoted it. Freedom from slavery != equality before the law) with the compromise election of Rutheford B. Hayes in 1876. The price for southern support in the electoral college - then end of reconstruction. In the north, counties with a strong quaker demographic that had been calling for abolition a generation earlier where breeding grounds for the KKK - by the turn of the century, sundown towns existed in all 50 states.
But up until the 60's, there were conservatives and liberals in BOTH parties, as they were parties that were mostly partitioned along OTHER lines - Catholics: Democrat. WASP - Republican. Northeast: Republican, Southeast: Democrat, Plains States: Democrat. Free Silver: Democrat, Gold Standard: Republican. The two parties where heavily regional and tribal. Obviously, there are exceptions to this, but, by and large, these were the stereotypes.
AFTER 1964, the great shakeout of the Republican and Democratic parties began, as the NEW primary axis of partition was conservative vs. liberal. Senators like Strom Thurmond moved from the Democratic side to the Republican - and states that had been Democratic strongholds for well over a hundred years, such as North Carolina, suddenly began electing conservative Republicans such as Jesse Helms. In the Northeast, the 'Rockafeller Republican' has almost completely vanished.
So yes, I find your argument unpersuasive and honestly, little more than an exercise in question begging.