The totalitarian must destroy politics and in its place substitute terror. He is but a tool in the hands of destiny. Those who give themselves over to an ideology go on automatic pilot as the corpses mount. Others then become merely grist for one's mill. That, oddly enough, is what social science of a certain sort yearns for too.
Human action falls outside the reach of such methodology.
Arendt saw this as the diminished and diminishing enterprise that it was. One problem with philosophy's relation to politics is that the philosopher is often driven to conclusions by his own internally consistent system. Here again, Arendt presses one of those analogies that distressed so many. Philosophy is similarly suspect to the political thinker, in part because of its drive to systematize, to reach inevitable and exhaustive conclusions. This helps one to understand why Arendt avoided calling herself a political philosopher.