I just say that you have to look at things in historical context. The Weimar Republic had a series of attempted communist uprisings and one or two major ones. They had communists machine gunning people in the streets while barricaded inside their communist newspaper building. "No way, I've never heard about this." Seriously look it up, they had to bring in artillery and literally shell parts of Berlin to stop them. I've found that people being so astounded that they never heard a word about this in history class will usually compel them to either look it up or read what you send them because they think you're lying.