The main problem with universal care is lack of order - who receives care when, where, and why.
Pricing allows society to determine how resources should be allocated. The US does not have enough resources to give everyone an MRI, CT scan, or even a doctor's visit whenever they feel like it.
There will never be an equal level of care that many are pushing for. The best way to determine who gets what is to let people know what the costs are for each procedure/visit. This will reduce the moral hazard problem.
http://en.wikipedia.org/wiki/Moral_hazard
Insurance should be used to pool risk together and not used to determine what care people receive. Insurance companies should very clearly provide insurance for specific high-risk events such as cancer or heart-attacks. This will reduce the BS that the insurance companies can use to say "oh, it's not covered in the plan."
Low-level stuff should not be included in the insurance package. Forcing people to open their pocketbook when they go to the doctors will incentivize people to take care of themselves.
Well, you ask, what about the people that can't afford insurance... well they have to get in the back of the line. If they come to ER with bullet wound without insurance, ok we treat that, but maybe we garnish % of your wages until some of it is paid off.