The US Government in the Health Insurance business? The arguments, when you can get down to those that are A) Real and B) Relevant, are varied. I've had a bit of difficulty drilling down to this list but think I've come to the gist of it.
It will be too expensive. Not only will it cost more for taxpayers and employers, but private insurance holders will see premium increases!I didn't find much data to back up any part of this statement. I expected to find short term, up front increases with long term and periphery cost decreases. What I in fact found was both short and long term savings, and with periphery costs (lower overall costs to treat due to better health resulting from access to health care, less costs due to decreasing stress levels) included the savings would be enough to make an oil company drool with envy.
Survey Shows Private Health Insurance Premiums Rose 11.2% in 2004Premiums Increased at Five Times The Rate of Growth in Workers’ Earnings and Inflation. About Five Million Fewer Workers Covered By Their Own Employer’s Health Insurance Since 2001.
Kaiser Family Foundation In the U.S., job insecurity equals health insecurity. Without significant subsidies to buy into COBRA, most unemployed workers will also quickly morph into uninsured workers. Healthpopuli .com
For the seventh straight year, premiums for employer-based health insurance rose more than twice as fast as overall inflation and wages, an annual survey of employers shows. (2006) McClatchy Newspapers
Workers face more cost-sharing in the form of higher deductibles and co-pays. (2008)
American Medical NewsAnd then there are the peripherals....Health Care Scandal has Real Victims. The U.S. health care system is an open scandal. We devote far more of our national income to health care than any other industrial nation. Yet we get worse results -- higher child mortality, higher deaths from breast cancer, less prevention and more expense. If you have wealth, the best medicine in the world is available to you. If you are poor, or increasingly a middle- or low-income family, too often you will lack insurance or be vastly under insured. You will forgo costly tests and let illnesses fester until they become debilitating.
Chicago Sun TimesHidden Costs of Health Care Report. Rising deductibles, Higher Co-payments and Escalating out of pocket costs.
Healthreform .gov
Pharmaceutical Companies

Insurance Companies
That's it for part one, "It's too expensive!" Stay tuned for "It's too Controlling!"