The opposition to public health care in the US is for three reasons.

One, it is the most profitable business in the country, and the fastest growing, and those who benefit from it (or fancy themselves as members of that class) don't want it to stop. It supports an immense parasitic administrative infrastructure which constitutes a vast constituency in favor of its perpetuation and growth.

Two, most privately insured individuals in the US are insured through their jobs, with their employers picking up at least part of the tab. Employers help subsidize the insurance industry, allowing costs to spiral much higher than they would otherwise. Insurance companies WANT medical costs to escalate, because it ensures future markets for their services. And service providers have no incentive to cut costs because they will always get paid. The system feeds on itself.

Third, since losing your job means losing health care for your entire family, it acts as a means of intimidating and controlling the workforce through threat and coercion. Many people are confident they have the skills and reputation to work anywhere, and the resources to afford a hiatus from work while they seek a new job. The need for health insurance keeps them docile and cowed and afraid to exercise their freedom of choice.

The cost of national health care will be enormous, but I suspect it will
be much less than what it is already costing us.