When we think of a criminal, we imagine someone with criminal motives. And when we look at Eichmann, he doesn't actually have any criminal motives. Not what is usually understood by "criminal motives." He wanted to go along with the rest. He wanted to say "we," and going-along-with-the-rest and wanting-to-say-we like this were quite enough to make the greatest of all crimes possible. The Hitlers, after all, really aren't the ones who are typical in this kind of situation--they'd be powerless without the support of others.