WHY did many plantation owners believe it was okay to use enslaved laborers?

Because of the economy.

Explanation:

Cotton played such an essential role in the cotton economy that the people completely neglected the slave labour force. Slavery was so ingrained in society that even poorer whites who could not afford slaves supported this practice. In this way, they racially equated themselves with the slaveholders and viewed as comforting the fact that they were not in a position as black people, and they were afraid of the uprising. The slave economy, which rested on slavery, had an international spread and the United States was the largest and best cotton producer in the world. Slavery shaped the culture and society of the South, which rested on the racial ideology of white supremacy. And importantly, many whites believed that slavery alone sustained the newly prosperous southern economy.

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