We are not told of what, precisely, Guzman Bento is ignorant in Don Jose's mind.
We are thus free to supply the larger answer that Don Jose probably did not intend:
Guzman's ferocity derived from his "ignorance" of the destructive power
of the supposedly beneficent dream-ideal -- a "fault" common to Charles
Gould, Don Jose himself, and almost every other character in the novel.