Three main sources. (But first the disclaimer About Isn't About You seems relevant--that is, even if medicine is all a sham (which I don't believe), participating in the medical system isn't necessarily a black mark on you personally.)

First is Robin Hanson's summary on the literature on health economics. The medicine tag on Robin's blog has a lot, but a good place to start is probably Cut Medicine in Half and Medicine as Scandal followed by Farm and Pet Medicine and Dog vs. Cat Medicine. To summarize it shortly, it looks like medical spending is driven by demand effects (we care so we spend to show we care) rather than supply effects (medicine is better so we consume more) or efficacy (we don't keep good records of how effective various doctors are). His proposal for how to fund medicine shows what he thinks a more sane system would look like. (As 'cut medicine in half' suggests, he doesn't think the average medical spending has a non-positive effect, but that the marginal medical spending does, to a very deep degree.)

Second is the efficiency literature on medicine. This is statisticians and efficiency experts and so on trying to apply standard industrial techniques to medicine and getting pushback that looks ludicrous to me. For example, human diagnosticians perform at the level or worse than simple algorithms (I'm talking linear regressions, here, not even neural networks or decision trees or so on), and this has been known in the efficiency literature for well over fifty years. Only in rare cases does this actually get implemented in practice (for example, a flowchart for dealing with heart attacks in emergency rooms was popularized a few years back and seems to have had widespread acceptance). It's kind of horrifying to realize that our society is smarter about, say, streamlining the production of cars than we are streamlining the production of health, especially given the truly horrifying scale of medical errors. Stories like Semmelweis and the difficulty getting doctors to wash their hands between patients further expand this view.

Third is from 'the other side'; my father was a pastor and thus spent quite some time with dying people and their families. His experience, which is echoed by Yvain in Who By Very Slow Decay and seems to be the common opinion among end-of-life professionals in general, is that the person receiving end-of-life care generally doesn't want it and would rather die in peace, and the people around them insist that they get it (mostly so that they don't seem heartless). As Yvain puts it:

Robin Hanson sometimes writes about how health care is a form of signaling, trying to spend money to show you care about someone else. I think he’s wrong in the general case – most people pay their own health insurance – but I think he’s spot on in the case of families caring for their elderly relatives. The hospital lawyer mentioned during orientation that it never fails that the family members who live in the area and have spent lots of time with their mother/father/grandparent over the past few years are willing to let them go, but someone from 2000 miles away flies in at the last second and makes ostentatious demands that EVERYTHING POSSIBLE must be done for the patient.

Once you really grok that a huge amount of medical spending is useless torture, and if you are familiar with what it looks like to design a system to achieve an end, it becomes impossible to see the point of our medical system as healing people.

[edit]And look at today's Hanson post!