Slavery was an abuse of power by government. The abolition of slavery was an abuse of power by government. If you are opposed to slavery, then you are in favor of abuse of power by government. If you are opposed to abuse of power by government, then you are in favor slavery, and therefore are in favor of abuse of power by government.
You are not opposed to abuse of power by government unless you are opposed to slavery and opposed to the methods by which slavery was abolished.
Could slavery have been abolished by different methods which did not involve abuse of power by government?
The constitution should allow states to nullify federal laws and court decisions, so that the free states could have nullified the fugitive slave act and the dred scott decision.
The constitution should require that federal police and military activities within a state require the approval of the state government, so that the federal government could not have used the Virginia militia to impose martial law and search for escaped slaves in Boston in the 1850s.
The constitution should allow people who are dissatisfied with their state to secede from the state and create a new state. The slaves should have seceded from the slave states and formed exslave states.
The slave states might have been reluctant to accept the new exslave states. Any problems which occur would be a dispute between different states. Resolving disputes between different states ought to be the primary function of the federal government. If the slave states refused to accept the exslave states and attempt to enforce slave laws in the exslave states with the police and militia of the slave states, then the slave states would be attacking the exslave states. Whenever one state attacks another state, the federal government should intervene and send the federal army to defend the state which is being attacked.
Even after slavery was abolished, some states continued to discriminate against african-americans. This problem would not have occured in exslave states.