From Erik Larson’s In the Garden of Beasts: Love, Terror, and an American Family in Hitler’s Berlin, which is worth getting from the library (this section deals with 1933):

It was one thing to read newspaper stories about Hitler’s erratic behavior and his government’s brutality toward Jews, communists, and other opponents, for throughout America there was a widely held belief that such reports must be exaggerated, that surely no modern state could behave in such a manner. Here at the State Department, however, Dodd read dispatch after dispatch in which Messersmith [the Consul General] described Germany’s rapid descent from democratic republic to brutal dictatorship. Messersmith spared no detail—his tendency to write long had early on saddled him with the nickname ‘Forty-Page George.’ He wrote of the widespread violence that had occurred in the several months that immediately followed Hitler’s appointment and of the increasing control the government exerted over all aspects of German society.

People in the 1930s simply couldn’t believe that Germany would act as it did. This might be one reason why cell phones and cell phone cameras are so powerful: it’s very hard to deny video. If cell phone cameras had been widely available in 1930, could the Holocaust have unfolded as it did, in a major Western country? The answer, of course, will always be “maybe,” but I think the shock of seeing footage of Jews and others being beaten and murdered in the streets might have had a powerful effect around the world.

I wonder if we’re on the cusp of seeing cell phone cameras reduce the amount of police brutality in public places, since police will know they’re likely to be taped. Cops don’t like this (see here and here for more).

Although I obviously love reading, it’s relatively easy to deny a written description of an event. It’s much harder to deny a video that shows the people involved. That’s not to say video can’t be manipulated—it obviously can—but sometimes a short video can do what “Forty-Page George” can’t. It’s hard or impossible to “exaggerate” video, even if it can be maliciously edited. We should still read, as “Twilight of the Books” makes clear, but video still changes things (it changes what can happen in fiction, for example; people have been writing about blue movies or explicit pictures for a long time, but the plausibility of something like Anita Shreve’s Testimony depends on widespread access to inexpensive video equipment (see also Caitlin Flanagan’s somewhat misguided but interesting essay on the novel). That’s relatively recent, and we’re still dealing with what it means.)

EDIT: See also this discussion of police and cameras from Crooked Timber.