Why were Whites in the South so against Blacks having the right to vote?

Because if the blacks got the right to vote they would vote for laws to end the cruelty of slavery and benefits which would include their freedom.

They didn't want to give up their superiority

Explanation:

African Americans were brought to the America's to be slaves, which they were for a very long time. They were looked down on by white people. It was until after the Civil War that the 13th, 14th, and 15th Amendments were passed and gave African Americans equal rights. The 13th Amendment banned all slavery and involuntary servitude, the 14th Amendment allowed all males over 21 the right to vote, and the 15th Amendment said that the right to vote "shall not be denied ... on account of race." The South, which was a huge slavery supporter, built its economy on slavery. Once the 13th, 14th, and 15th Amendments were passed, their way of life was ruined. Their economy crashed as well as their culture for decades maybe even centuries. But Southerners were strong believers of whiter superiority, which means that white people were better than everyone else who is not white. They believed that African Americans, their former slaves, participating in government was wrong and it just brought out the racist attitudes of the entire South. Mind you, the South was against the amendments, but were forced to pass them due to the Federal Government.