The 1917 Revolution gave birth to both the reality and the myth of the Bolsheviks and the democratic left. The social democrats rejected the violence which was part of the communist party. They claimed to follow a democratic path to socialism. They turned Marx into a wise man that should not be taken too literally.
A coalition against fascists arose. Social democrats made common cause with the communists. There is reason to suspect that Stalin knew what he was doing bringing Hitler to power. Since the 1930s the enemy of the left has been fascism. The social democrats successfully split from the communists. The end of the cold war looks like the end of WWII. The left won the cold war. The right disappeared.