What we knew, as serious students of medicine and toxicology, is that a toxin has a threshold for causing injury and the subject has a profile of variable susceptibility that changes the threshold.
Clearly those two factors interact and result in an expression of the toxic effects that varies.
This is about a Lancet study on healthy smokers–and there are plenty–in fact it is not correct to say healthy smokers are rare, particularly smokers who don’t smoke much. In the Peto and Doll study of physicians, the group that smoked less than 10 cigarettes a day had better health and mortality outcomes.
Risk for smokers for heart disease and pulmonary disease is higher, but not 100%. That kind of thing just doesn’t happen in biology.
It is also bad science to count every smoker who dies as a smoking death–which is how the fanatics do it to puff up their numbers.
So, for example, there are many smokers who live long lives with no apparent health harm from smoking, no cancer, no COPD.
On the other hand genetic predisposition to lung disease is undeniable, with the most sever known propensity to lung injury the alpha one anti-trypsin deficiency, that produces COPD in non smokers and more sever smoking susceptibility.
Asthma is also a factor and sensitivities that produce reactive airway disease.