You make some good points, but you ignore a lot of history. You’re right that the Republicans were the party of emancipation and the Democrats were the white southern racist party. But since Johnson pushed through the Civil Rights Act and the Voting Rights Acts in 1964–1965, there has been a shift in the parties. Nixon solidified that shift with his southern strategy, essentially telegraphing through racist dog whistles that white supremacy was welcome in the Republican party while not in the Democratic party. While there are certainly racists within the Democratic party, the Republicans have no equivalent to Barack Obama, Kamala Harris, Corey Booker, Stacey Abrams, etc… Times have changed. If you care about stopping racism, the place to do it is in the Democratic party, not the Republican.