I can't say I know anyone who's indulged reiki, but I've got a lot of flak from my brother telling me that cannabis cures cancer, when I told him that I was doing chemoradiotherapy for my Stage 3 rectal cancer. Today I've finished a cycle of six weeks of treatment, and while I'm extremely tired, the signs are good that it's in remission. If I'm lucky, I'll have a full pathological response, i.e., it's gone.
Despite the number of people who go through cancer, it's rarely brought up in polite conversation. It wasn't until I got it myself that all manner of people came out of the woodwork to talk about how someone they knew had gone through the same thing. Many of them have been using concentrated cannabis oil (which my brother also said I should do). After reading a couple of studies, it does have a positive effect on cancers, but the level depends on the type of cancer. In the case of colorectal cancers, it seems to stop the cancer but not kill it, most likely due to the CB1 receptors in the tumour being hypermethylated (as in, the gene isn't being expressed). The level of evidence isn't that of a systematic review, but it's enough for me to give it a go and certainly enough for further research. Unfortunately, the two sides of the argument seem to think that it either doesn't do anything (there's not enough evidence) or that the medical establishment is just a ruse and that cannabis cures all cancer. I prefer to use my critical thinking skills and get the best of both worlds.
I can understand why people might indulge in quackery - I've got surgeons telling me they need to cut out my rectum and part of my lower intestine, even with a full pathological response. Possible side effects are shitting 3 times a day (not so bad) and erectile dysfunction (worse). This has been the gold standard of care for 15+ years now, and the surgeons don't give a fuck about my quality of life, they just want to cut. There's mounting evidence to show this might be overtreating the problem, and that you can get away with a heavier dose of chemo with the radiotherapy. Frankly, I don't want anyone cutting anything out of me unless it's absolutely necessary, but it's hard finding an advocate who would be willing to tell the surgeons to fuck off.
I'm lucky, in this sense: I understand the research and I have access to upcoming studies (I used to work at an institute that did systematic reviews of evidence). Most people won't have such advantages, so they just sit there and do what the surgeons tell them to do, as if they don't have any options other than no treatment. If that's all the choice I got, I'd be wary of the medical establishment too.