The Sherman Antitrust Act, Clayton Antitrust Act and the Federal Trade Commission Act were enacted to protect consumers in many ways: among them to enforce competition among producers to prevent or end monopolies.
The underlying reason for these monopolies is that the infrastructure carrying the service is private. Cable companies must build and maintain their own infrastructure. This infrastructure is such a large barrier to entry that it effectively removes competition and creates regional monopolies.
The government has a responsibility to ensure fair pricing, quality control and to protect the consumer in situations where the free market fails. Similar services (power, gas, electricity, water) were once private until better, publicly owned, service was available.