Don't confuse economics with politics. Many Southerners were anti-slavery on a moral basis, but owned slaves for economic reasons. Those economic reasons were ultimately doomed by increasing mechanization.
"If" the Republicans had campaigned to free the slaves and re-imburse the owners monetarily, the Civil War probably would not have happened. But they did not...they simply wanted to issue an edict.
The result of their NOT doing so was probably more expensive to the country than re-imbursement would.