Abolitionist ?

1. The act of doing away with or the state of being done away with; annulment.
2. Abolishment of slavery.

John Brown was an abolitionist and didn't approve of slavery.

"I have possession now of the Untied States armory, and if the citizens interfere with me I must only burn the town and have blood."
A contingent of U.S Marines , commanded by Colonel Robert E. Lee, rushed from Washington, D.C., to Harpers Ferry. Outnumbered, Brown surrendered , and a Virginia court sentenced him to death. Many Northerners saw Brown as a martyr in a noble cause.

Henry David Thoreau declared ,"He is not old Brown any longer," he said, "he is an angel of light."