Re: It really depends on how it's done.
Why are 40+M US people without health insurance for at least part of the year? Is it mainly due to changing jobs? Aren't there federal or state programs designed to ensure coverage continues between jobs? Are they working or not? Why are the poor lacking health insurance? Is it just lack of money, or is it lack of money-handling skills, or something else? What type of insurance would be necessary and beneficial for those who don't have it now? What should it cover, and what should not be covered? Should private companies provide it, or should it be a single, national system? Why or why not?
Generally the poor don't have medical coverage because in the US, because if the company you work for doesn't provide it you probably can't afford it. For a number of reasons buying insurance for yourself is much more expensive then a company doing so for it's employees. Worse, because the market is designed to sell to companies, it can actually be hard to find out about plans for individuals or what the details of those plans are.
Cobra, the plan that lets you stay on an old jobs coverage, requires you pay whatever the company does for the coverage, plus a paperwork charge plus whatever you where paying to begin with. This means that it tends to be one of the first things that unemployeed people drop when their money begins to run short. Cobra works, but it would work a lot better if the government subsized part of the payment costs for a period.
Jay