Ma Health Insurance

It boggles my mind that the proponents of a government run health insurance entity would actual state that this entity would bring competition to the insurance arena. How would these private businesses compete with someone who does not have to pay taxes. How do companies compete with an entity that can literally raise taxes to pay for operational costs or an entity that is funded non voluntarily by the citizens of the United States? Can the private insurance companies pass legislation that changes the rules of the game in the insurance business? No but the government could certainly dictate the rules of their own business by passing legislation in its favor. Can someone please give me a logical reason as to how this government run health insurance option would do anything other than run private insurance into the ground to ultimately pave the way for the government to be the only health care option?