Dr. Cameron was about to bash in the head of his daughter, Margaret because he was angry and afraid when he saw the African Ameifcan man touching Margaret. The fears about intermixing are being referenced here are that intermixing is terrible and that that will lead to a lower class person. The fear is that they want to preserve the white race. The other woman he was about to hit was an older woman, who I think was his wife.
The last scene of a city on the hill, people living in paradise with Jesus is Griffith communicating his beliefs. Griffith is saying that white supremacy should be the law through this scene. He is saying that the only people who are worthy, innocent and righteous are white people. He believes that the world will be calm and at harmony if everyone is white, he believes that Jesus is white and that equals pureness.
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