Things we believed during the Cold War that ended up being wrong

Communists were always the enemy
Geopolitics is a messy business. During the Cold War, Western media might have tried to act like Communists were always the enemy, but even at the time this was clearly untrue. That's not meant in some airy, fairy "everyone's a good person" way. At various points in the Cold War, NATO countries were working with and actively courting Communist leaders — including some who were so far off the deep end that calling them bats–t would be an insult to guano.