Efficiency at solving the problem at scale. What good does it do to have the most efficient system in terms benefit per dollar spent if it helps only a few people? Government is the most efficient at providing help at scale. For example helping Ukraine defeat Putin requires government and not charity. Want clean water across the country? Need government intervention. Want to provide universal healthcare? Need government intervention. Want everyone to read and write? Need government intervention. Charity is not sufficient to provide the needs of the populace. For one thing, relying on charities quickly runs into the free rider problem.