Do you think he's not one? Cause practically every analysis of that movement's intellectual side identifies Spooner and Garrison as the leaders. They're about the only two who consistently make the history books as well, plus Stowe I suppose as the literary side and Brown as the violent domestic terrorist branch of the movement.
This is the same man who wrote "A Treatise on the Unconstitutionality of American Slavery"
Very good! You know your history!
where he had little to say about the kind of men who would become the leaders of your confederacy.
That is nice and all, but completely misses his post-war book quoted from here. His critique of the northern participants in the war and after the war (as in the people you constantly defend, embrace, and promote) is one of the most scathing pieces he ever wrote.
I'm perfectly content with ceding that he was no friend of the south and that makes his testimony here all the more amazing. But even then as a staunch opponent of slavery, I don't believe he ever called Jefferson Davis the "chief murderer of the war." No, he saved that title for Ulysses S. Grant.