I have often seen mention of lynch mobs, insurgents like the KKK, and awful attacks and raids on black communities and abolitionists perpetrated by white supremacists, but very little to suggest that anti-slavery activists, ex-slaves or slaves themselves engaged in the same sort of tactics.
Was there ever an organised faction that sought to strike back at groups like the KKK? I can't imagine that there wasn't some sort of reprisal for the vile acts white supremacists committed during this era, was it just that such reprisals weren't undertaken by a specific group and were more sporadic?
Also please remember Rule #1 in your responses, I'm asking this out of pure academic curiosity.
Militant abolitionist John Brown was well known for engaging in direct action against slave owners in Kansas, Missouri, and most famously at Harper's Ferry. His actions went through various iterations of formality and hierarchy, but he certainly believed in using violence and material action to create not just better outcomes for slaves (he freed many slaves and killed or captured many slave owners) but also in spreading the good word of abolition as well as encouraging or inciting slave revolt. Ultimately, he was unable to ignite a coherent movement and was hanged for his illegal actions (I encourage you to read about all of his exploits, but Harper's Ferry ended up being his last hurrah and his downfall.)
However, in some instances he has been cited as igniting the militarisation of slave owners and kicking off the Civil War - of course it would be insincere to pretend there weren't numerous factors and agitators on both sides, but the effect of his actions shouldn't be understated either.
An expert on this period of American History may be able to flesh out this chapter, as well as any other anti-white supremacist like you've asked, but John Brown came to mind immediately for mine, an underrated abolitionist hero in my reckoning, and I think fits the bill as posited in your initial question.
For an in-depth look, this book is pretty good:
Reynolds, David S. John Brown, Abolitionist: The Man Who Killed Slavery, Sparked the Civil War, and Seeded Civil Rights. New York, New York: Vintage Books (A Division of Penguin Random House LLC), 2006.
More accessible reads:
Bordewich, Fergus M. “John Brown’s Day of Reckoning: The abolitionist’s bloody raid on a federal arsenal at Harpers Ferry 150 years ago set the stage for the Civil War.” Smithsonian Magazine. (October 2009) https://www.smithsonianmag.com/history/john-browns-day-of-reckoning-139165084/
Brown, DeNeen L. “‘Unflinching’: The day John Brown was hanged for his raid on Harpers Ferry.” The Washington Post, (2 December 2017). https://www.washingtonpost.com/news/retropolis/wp/2017/12/02/unflinching-the-day-john-brown-was-hanged-for-his-raid-on-harpers-ferry/