“How easily people fall into hatred. How easily people throw hoaxes and lies. Because they know that nowadays people are also easily instigated, manipulated and agitated.”
Related quotes

"Sports" in How the World Works, p. 169
Quotes 1990s, 1990-1994, Secrets, Lies and Democracy, 1994

“People can so easily be tempted by slackness… and by money.”
Source: The Diary of a Young Girl

This misquote could possibly have two possible sources: an abridged version of a paragraph in Mein Kampf regarding the Big Lie, or a report by the United States Office of Strategic Services about Hitler's psychological profile http://www.nizkor.org/hweb/people/h/hitler-adolf/oss-papers/text/oss-profile-03-02.html. The second version is very close to an actual quote by Joseph Goebbels.
Misattributed
Variant: The bigger/more blatant a lie, the more people will believe it.

A Mortal Antipathy (1885) This statement is often misquoted as "Love is the master-key that opens the gates of happiness".

“Socialism is easily understood by any child; it is taking other people's stuff.”
2010s, Socialism's Legacy (2011)

"The antiscientifical revolution and mathematics" (1998, Vatican).

Book 1, Chapter 39
Discourses on Livy (1517)
Context: Anyone who studies present and ancient affairs will easily see how in all cities and all peoples there still exist, and have always existed, the same desires and passions. Thus, it is an easy matter for him who carefully examines past events to foresee future events in a republic and to apply the remedies employed by the ancients, or, if old remedies cannot be found, to devise new ones based upon the similarity of the events. But since these matters are neglected or not understood by those who read, or, if understood, remain unknown to those who govern, the result is that the same problems always exist in every era.