I don't think consensus-building is necessarily bad on it's own. Depending on the environment, when people don't feel like they have an opportunity contribute, it can potentially lead to other issues.

To your point, I think a lack of leadership can kill a consensus-building process. Whoever is coordinating needs the authority and will to end the discussion when the time is right (among other things.) Otherwise, it really can become endless debate and drawn out attempts to get some unwilling party onboard.