Active competition in the marketplace is essential for the effective operation of a market economy. Competitive markets force business firms to produce the products that consumers demand at the lowest prices that will cover costs. Although the other answers might help a market economy to work well, a market economy could function without any of them. Social responsibility of business leaders. Careful planning and coordination of market activity.
Individuals understand what is in the public interest.
A market economy relies on competition to assure that if consumer demand goes up, increased output is supplied at the lowest prices that will cover all costs of production and still leave a reasonable profit. Thus, competitive markets play a stronger role than any of the forces proposed in the other answers. Employment would go up. Employment would go down. Employment would stay the same.