For it to be a monopoly, well, there would have to be only one or two medical insurance companies.
There are not.
Also, ridiculous laws limiting the public's options in terms of purchasing said insurance only serves to create such problems as localized/statewide insurance monopolies.
And government control of health care would be a goverenment monopoly...especially after they put the private sector companies out of business.
Yep, irony is a bitch.