Dude, it's called "Commonality of Sin"; it's an ancient and venerable rhetorical strategy. Saint Paul said "Christ Jesus came into the world to save sinners; of whom I am chief". The most famous practitioner was Saint Augustine whose main propaganda work was literally named "Confessions". Google AI writes:
Why Speakers Use This Specific Tactic
1. Neutralizing Defensiveness: By saying "we are all guilty," the speaker lowers the target's shields. It is rhetorically difficult to argue "I am innocent" when the person leveling the charge has already readily conceded their own guilt.
2. Establishing Moral Authority: Confessing to the flaw first paradoxically grants the speaker the authority to lecture others about it. It frames the speaker as honest, self-aware, and objective.
3. Coercing Agreement: It forces a logical trap. If you reject the accusation, you are framed as lacking self-awareness; if you accept it, you have validated the speaker's original charge against you.