"During the war with England [in 1812] a circumstance occured that in the end made him a most determined Abolitionist: & led him to declare, or Swear: Eternal war with Slavery. He was staying for a short time with a very gentlemanly landlord since a United States Marshall who held a slave boy near his own age very active, inteligent and good feeling; & to whom John was under considerable obligation for numerous little acts of kindness. The master made a great pet of John: brought him to table with his first company; & friends; called their attention to every little smart thing he said or did: & to the fact of his being more than a hundred miles from home with a com-pany of cattle alone; while the negro boy (who was fully if not more than his equal) was badly clothed, poorly fed; & lodged in cold weather; & beaten before his eyes with Iron Shovels or any other thing that came first to hand. This brought John to reflect on the wretched, hopeless condition, of Fatherless & Motherless slave children: for such children have neither Fathers or Mothers to protect, & provide for them. He sometimes would raise the question is God their Father? . . ." (From a letter John Brown wrote to 13 year old boy named Harry Stearns, he's referring to himself in the 3rd person)
Completely agree, from what I've read, the John Brown is crazy argument originates from southerners trying to prevent Brown from becoming a martyr and northerners trying to convince the south this was a one time event and to prevent succession. Reading about his early life, it's clear from a young age he had these views and saw himself as acting in the service of the lord in stopping slavery. There's a good quote from abolitionist Wendell Phillips that describes the whole period perfectly "hard to tell who’s mad."