There's still a huge group-bargaining incentive, although, I agree, it would be a move in the right direction.
This is one reason I'm in favor of government health care: The profit motives of private health care favor denying care, since not paying out money is a good way to make money. So you have case where nobody will cover you for arbitrary reasons, or deny you payment due to a "pre-existing condition" or some other nonsense.
Would you favor the nationalization of all types of insurance or just medical? Doesn't auto-insurnace have the same evil profit motive?
This is an argument against all private insurance (home, auto, etc).
As for power lines.. well, there haven't really been any conclusive studies in this area. But you get the point.
Same-environment shouldn't be a factor, as long as the reasons the environment might impact health are/can be known.
I'd argue that nobody should be living somewhere that might have health risks involved (e.g., underground oil spills, toxic ash, a radioactive waste storage facility a block away from the elementary school .... in other words, williamsburg/greenpoint brooklyn).