We suggest that as social cohesion improves, the macroeconomic gains from progressive redistribution decline. Social interactions facilitate diffusion of nonrival knowledge. The consequent bridging of the knowledge gaps makes learning cheaper for children with limited access to adults with high human capital and thereby lowers the optimal progressivity for a redistributive policy. If social cohesion exceeds a critical threshold then zero progressivity would be optimal. Numerically, a country with greater social cohesion finds smaller gains in growth, efficiency, and welfare from progressive redistribution over and above the gains from a Pigouvian subsidy that eliminates the inefficiency caused by knowledge externalities.