His extreme views: Brown's views on race were also controversial. He believed that the only way to establish racial equality in the United States was through violent revolution. He was also a strong advocate for the rights of Native Americans and believed that they should be given back their lands.
His connections to abolitionist groups: Brown's affiliation with various abolitionist groups made him a target of criticism. Abolitionist groups were strongly opposed by many people in the United States, who saw their efforts as disruptive and dangerous. Brown's connections to these groups made him an even more controversial figure.
His impact on the Civil War: Brown's raid at Harpers Ferry is considered by many historians to be a catalyst for the Civil War. The raid heightened tensions between the North and South and helped to bring the two sides closer to war. Brown is therefore seen by some as a controversial figure for playing a role in the start of the Civil War.