Chemotherapy is a research-backed approach that has been constantly refined since it was first used roughly 100 years ago.
Bloodletting is a theory-based approach and was, as far as we know, in continuous use for thousands of years despite being ineffective for almost every single condition.
The key difference is precisely the research and constant refinement, not any particular mechanism of action.
Bloodletting is not ineffective at all. If you have a dangerous bacterial infection, and have no sulfa drugs and no modern antibiotics, bloodletting is a good idea. You are reducing iron availability. Human tissue can cope with low iron. Bacteria need quite a bit of it critically to reproduce.
>In theory Chemotherapy is a research-backed approach. In practice it is simply the best we have for those that reject proper nutrition and exercise.
Cancer is the result of DNA damage, which you can get from viruses, chemicals (of all types), sunlight, and even background radiation. Plus, I suspect, random errors in DNA transcription. That's why your body has multiple overlapping systems to detect and destroy cancerous cells.
The idea you'll never get cancer if you just eat right and exercise is a fool's hope - if you don't die of something else first you'll get cancer.
And yes, chemo isn't ideal, but it will normally stretch your life out some. It's certainly not the best we have in all cases - there are targeted drugs for some cancers now.
This is not at all the same thing. Ancient medicine was pre-scientific method and therefore they were throwing things at the wall and seeing what would stick with no eye to all the problems of informal research (confirmation bias, survivor's bias, correlation!=causation, etc.)
Modern Chemotherapy isn't someone just presuming something works through informal testing, void of any understanding of the fundamental mechanism by which it works.
It is a necessary evil. Chemotherapy is more akin to amputation of irretrievable mortified flesh than to blood letting.
Medicine did not start advancing rapidly until around 1800 when people first started using statistics to determine what worked and what didn't, rather than anecdotal evidence.
Bloodletting is a theory-based approach and was, as far as we know, in continuous use for thousands of years despite being ineffective for almost every single condition.
The key difference is precisely the research and constant refinement, not any particular mechanism of action.