For the health care bills that are now being debated in the U.S., I think there are two legitimate arguments against the "public option."
(a) It is too expensive. (President Obama is deliberately underestimating the cost by at least a factor of ten, in my opinion. Quite seriously -- do the math

-- the only possible way to pay for it is to stop fighting wars.)
(b) Anything the government is in charge of is bound to end up as a chaotic boondoggle. (Although Social Security and Medicare have not been badly run, all things considered.)
The argument in favor of the "public option" is this: however bad it may be, what we have now is worse.
This is what we have now. A poor person gets sick. He has no money so he does not go to the doctor. He gets worse. He still has no money so he still does not go to the doctor. Now he is really, really sick. His friends drop him off at the hospital emergency room. The hospital admits him, tries their best to keep him alive. He dies anyway, leaving behind a $100,000 hospital bill.
Who pays the $100,000? We do. To recoup its losses the hospital jacks up its rates for customers who have private insurance. The insurance companies raise the premiums. Medicaid pays a share, causing our taxes to go up. Everybody pays more for everything.
The patient? Social Security gives his family $250 toward his burial expenses.