Even if the claim were that Brown's motive arose from his adherence to Christian principles rather than a desire to proselytize, that claim would also be hard to support given the numerous axe murders committed by Brown and his sons.
John Brown was an unhinged fanatic who just happened to fixate on slavery as his excuse for unleashing his rage on others. I only regret that the POS could only be hanged once.
Hence Christianity is capable of producing unhinged fanatics...