I'm not sure how it is in various places, but around here employer connected insurance is generally all comers, with premium based on age only. Obviously premiums overall are affected by costlier and cheaper users - but that is true whether you're talking employer provided, singly/personally obtained insurance, or national healthcare. The whole point of health insurance (apart from catastrophic coverage) is spread the cost around. Otherwise there is no point.
Started 4/14/08 LINK TO PROGRESS PICS
"It is impossible to live pleasurably without living wisely, well, and justly, and it is impossible to live wisely, well, and justly without living pleasurably" Epicurus