I think Zinn would argue that Columbus was responsible for the behavior of his men. Zinn would suggest Columbus did not advocate one course of interaction with the Native Americans and his men "went rogue." Rather, Columbus was part of a larger historical belief of the time period that advocated subjugation and control of indigenous people as a part of historical conquest. Columbus and the Age of Exploration was a context in which the prevailing zeitgeist was to conquer and subjugate in the name of country. This was a cultural attitude that Zinn feels Columbus embodied in his actions and his condition of being. There was nothing to indicate Columbus being in opposition to this or defying this spirit. Rather, with his enslavement and control of Native Americans, Columbus embraced it.
This spirit of the day in what drove Columbus, animating Columbus and his men. Zinn would suggest that Columbus would have to be responsible for his own behavior and the behavior of his men because he embraced a spirit that sought to control indigenous people and not develop an inherent respect for them.