> Do you have a source for this claim?
It's my own opinion.
> It seems to me that in every case where "ideology" plays a large role in people doing horrible things to each other, one of the common threads is propaganda (often built around de-humanizing the opposing side). Post-WWII Europe might be the best example of what a society with "censored" or regulated propaganda looks like.
My argument is that you cannot trust anyone to apply a fair standard for which propaganda could lead to people doing horrible things to each other and which propaganda could not. The far greater risk is for such a mechanism to be hijacked by the very demagogues it is intended to disarm.
It's easy. First, you pick out the most extreme and unpalatable examples of your opposition. Then you scapegoat them as a public menace worthy of censorship. Then you exploit the powers of censorship you've received and apply them more broadly. The rise of Hitler[1], for example, followed this literal pattern--he convinced the people that the Communist Party was enough of a public threat that they should be banned, received the executive powers necessary to do so, and then banned the Social Democrats too, for good measure.
It's understandable that post-WWII Europe has the particular set of scar tissue necessary to prevent the rise of another Hitler. The only problem is that Hitler himself rose to power on the back of the scar tissue that post-WWI Europe developed to prevent the rise of another Lenin.