The Aggregate pricing only contains a price signal when participation is voluntary.
In this case the aggregate price reflects how the participant group values the service.
When participation is not voluntary the aggregate price only informs how the controlling interest values the service.
The non-voluntary members suffer the injustice of paying more then they would like for a service.
The problem is forced participation.
The colonoscopy is a good example of a procedure which on the macro level is low on the list of things that save lives. A planer, who will always be acting with limited resources, would be rational to not offer this service.
Colonoscopy's do save lives though and individuals have different medical budgets. Given different budgets it is rational for some to get colonoscopies while others should not.
I speculate that is is very rare to find a doctor who if you ask if you should get a colonoscopy will ask you how much money you make or what you medical budget is before giving you an answer.
Less Wrong readers are familiar with the idea you can and should put a price on life. Unfortunately the Big Lie that you can't and shouldn't has big consequences in the current health care debate. Here's some articles on it:
Yvain's blog post here (HT: Vladimir Nesov).
Peter Singer's article on rationing health care here.
Wikipedia here.
Experts and policy makers who debate this issue here.
For those new to Less Wrong, here's the crux of Peter Singer's reasoning as to why you can put a price on life: