Image: UbisoftOfficial screenshot from Ubisoft.
The Joys of Freedom is the story achievement for completing Memory Sequence 8 of Assassin's Creed Syndicate. You earn it by finishing Sequence 8, four memories that bring the twins close to Starrick himself.
Play the main memories of Sequence 8 through to the end. Optional objectives do not matter for this one; only the 100% sync achievement, Mentor, asks for those.