The question is: would the random mutation have occurred and have resulted in cancer anyway for most of those engaging in 'risky' behavior?
Suppose only breast cancer (in women), prostate cancer (in men) and lung cancer (in both genders) existed. Suppose further that breast and prostate cancer account for 60% of all cancers and that smoking doubles the chance of lung cancer, but doesn't influence the chances for breast or prostate cancer.
For any individual cancer patient, the chance that they were 'unlucky' would be much larger than the chance that their behavior was relevant to their cancer. This is true even for those that smoke. Especially for those that get breast or prostate cancer, but even for lung cancer it would be 50/50.
Suppose only breast cancer (in women), prostate cancer (in men) and lung cancer (in both genders) existed. Suppose further that breast and prostate cancer account for 60% of all cancers and that smoking doubles the chance of lung cancer, but doesn't influence the chances for breast or prostate cancer.
For any individual cancer patient, the chance that they were 'unlucky' would be much larger than the chance that their behavior was relevant to their cancer. This is true even for those that smoke. Especially for those that get breast or prostate cancer, but even for lung cancer it would be 50/50.