Insurance works best when everyone is paying into the big pool of money. The more healthy people paying in, the more that's available for the people who need it.. so I absolutely agree that the poorest amongst us should have insurance because honestly I think they'll get more benefit than those that can afford proper rest, nutrition, preventative measures, etc.
I honestly don't know enough about the medical industry to know how much knowledge and equipment is gatekept versus the need of expertise and other emergency equipment. I imagine it's a case of 'its fine if everything is going well, but if things go badly you'll want the experts and facilities'. I sincerely don't know how much is profit-driven versus how much is better for community health, that's why I think the profit motives are the bigger problem than the concept of insurance.