The Holocaust revealed humanity's capacity for unspeakable evil when ordinary people submit to authority - yet the same social-psychological mechanisms that enabled genocide can potentially prevent future atrocities. Experimental evidence from Milgram's obedience studies, Jane Elliot's discrimination experiments, and historical analysis of Police Battalion 101 demonstrates that individuals readily commit horrific acts when legitimate authorities sanction such behavior within hierarchical structures. However, Holocaust rescuer testimonies and helping behavior experiments show these same mechanisms can promote compassion and moral courage when authorities endorse prosocial action. By combining social psychological experimental data with historical case studies and child development research, this analysis reveals how individuals enter an "agentic state" in hierarchies where obedience trumps independent moral judgment, with childhood disciplinary patterns strongly influencing adult responses to authority. Rather than relying solely on moral education, preventing future genocides requires deliberately restructuring social institutions to promote prosocial authority through multiple reinforcing strategies: teaching about social processes, establishing mechanisms to challenge authority, developing empathy skills, using justice-oriented language, and engaging in concrete action. Understanding and reshaping these fundamental authority relationships offers the most promising path toward ensuring "never again" becomes reality.