Quantril was a terrorist also and recognized as such by history books.He used the excuse of war to carry out bandit raids on innocent civilians. In other words he was the northern equivalent of Brown.
Quantrill was an irregular, but was given a commission by the Confederacy. Also he did no worse than his Jayhawker Redleg opponents. Sen. Jim Lane for example.
The difference between him and John Brown, is that Brown had NO authority, and no state of war existed at the time.
Not all history books condemn Quantrill.