Eric,
I assume you mean unions as they exist right now, not unions as an idea? If not, then it seems somewhat patent why unions are necessary: they are a collective in an area of human activity (work and earning) that dominates our lives.
IMHO, its not true that unions are anachronistic, but the framework in which they could be effective is anachronistic in a world that is dominated by reductionist self-benefit based reasoning.
--ravi