Why did so many prominent white americans, from both the north and south, support the colonization of freed slaves?

 The whites believed that it would never be possible to achieve an equal society between the blacks and the whites as the slave institution had so much be embedded in the society. They posited black new concerns such as civil rights as those that would could insurrection. By colonizing the freed slaves the system would be maintained albeit in a better way.

Militarism is the answer.