When Anthem Insurance acquired Cigna Insurance in July 2015, this reduced consumer choice and possibly transferred negotiating power from the consumer to the insurance provider. But the merger also probably conferred some economic benefit on society by increasing the economy of scale.
These two possible effects are opposed from the perspective of the consumer. The consumer benefits from the economy of scale, but the consumer loses when negotiating power is reduced. So one could say the merger had good and bad effects to the consumer.
What is the net effect of the merger from the perspective of the consumer? Are consumers better off when mergers occur? Obviously monopolies are not good for consumers, so at what point do mergers approach monopolies and no longer have a net benefit to society?