Well, I just found out that the OED does not have an entry for either "rebartiveness" or "rebartive." Neither word occurs at all within the Corpus of Contemporary American English. And then I realized that I was spelling the word incorrectly -- the passage I submitted moments ago contained the correct spelling: rebartativeness. And that word IS in the OED. the state of being repellent, unattractive, or objectionable. So that dashes my amateur etymological hypotheses!
I haven't looked this word up in the OED yet -- it isn't in any of the books on my shelf. But I saw it in an article. I am wondering if it might come from "barba" in Latin (beard)-- in which case "rebartiveness" would mean something like 'a prickliness of temperament.' Or perhaps the noun is related to "batre" (French: to beat), "boter" (Old French: to butt, to strike), "batt" (Old English: cudgel), or "battuere" (Latin: to beat). In that case, "rebartiveness" would be 'the state or condition of beating back someone else's arguments or opinions. I assume there is also an adjective form, "rebartive," and probably and adverb, "rebartively."
I think that these approximate senses would work in the passage I read--but I could be wrong.
Here is the passage and citation, for your reference and use:
“It’s not just because both writers are from the slums of Oakland, California, that Williamson is such a passionate advocate for London. His white-hot scorn for literary fashion and indeed for most conventional criticism lights up nearly every sentence here. London managed to be both a socialist and a fascist, both a fervent champion of the oppressed and a militant racist, and Williamson revels in his hero’s contradictions. More than that, he identifies with London to a sometimes alarming extent, making this one of the least politically correct texts of our time. It’s also one of the best routes to understanding how London came by his extreme views (he was a writer who knew about injustice and exposed it even as he sometimes typified it), perhaps because Williamson doesn’t shy away from confronting their rebarbativeness.”
Anonymous (June, 2008). Cover to cover—Biography and memoir: Oakland, Jack London, and me, by Eric Miles Williamson (Texas Review Press). The Atlantic, p. 114. Retrieved on June 8, 2008 from http://www.theatlantic.com/doc/200806/new-books