Turns out it's a bit paraphrased.
"A statesman who aims at perfection, and thinks that he knows how to reach it, will stop at nothing to drive others along the same road, and his political ideals will be inextricably mixed up with his desire to remain in power. Perfection, in practice, is never attained, and the terrorism used in pursuit of it simply breeds the need for fresh terrorism. Consequently the attempt to establish liberty and equality always ends in the police state: whereas more limited aims, based on the realisation that man's nature is full of evil, may lead to a fairly decent society."
Is this a "bit paraphrased" by you or are you quoting someone quoting Orwell? I did a search for Orwell and Voigt and found this, but that is about it. All politicians and leaders, past and present, tend to think they are aiming towards a perfection that is carved from "goodness". The problem is, nobody ever thinks they're the villain in the movie of life. But, someone has to be. The truth is we are all Hero's and Villians alike (couldn't help myself with the BB's link). But it's the victors that get to write the script of history, which is part of the reason people pursue power so fervently, so that their vision is the one written about, passed along and sung aloud around the campfires of the future.