You are quite right pointing out in your editorial that cancer patients should not avoid medical treatments and rely on positive thinking alone.
But let's not put down good feelings and happiness in the process of discounting pop psychology and folklore. Cancer patients' bodies are being attacked insidiously, causing profound physical changes as well as changes in behavior and self-esteem. We all choose how we feel emotionally and if cancer victims can choose to be happy, how much better they, and the people around them, will feel.
A little knowledge about psychology may be dangerous, but hearing from medical science that it has proved my happiness and good spirits don't help me physically fails to make me feel any better either.