if they're using false identity?
if they're in the US illegally?
etc.
Use your imagination!!
what are reasons that some people refuse medical insurance and what demographic to you feel they fill?
2 answers
One of the things of concern to many is privacy. In the US, the privacy laws are widely ignored. If you have a serious disease, say HIV+, or mental diseases, the dr has to report these as treatment "codes" to the insurance company, which then in turn often allow employment companies to see them. It is not a trivial matter to carry these employees on the work force, as it increases health premiums. So if you don't want to be laid off, or be in an insurance database on health risks (often these are searched just as criminal records are searched) prior to job selection, one does not allow insurance companies to know these things. Ever wonder why it is difficult for HIV+ folks to get a job? Or folks who have been treated for emotional or mental disorders?