Unfortunately the flaw in that is that you are looking at simple emissions, the figures I looked at were estimates of what we actually breathe in, and most of us spend more time in our homes than our cars and modern homes lack adequate ventilation so that’s why the exposure in the home is so high. It’s like saying that sitting in your car in the garage with the garage door shut and the engine running you’re no more likely to die than driving down the road because the emissions are the same, clearly not because the concentration of gas is so much higher it will do you more harm. An extreme example I know but it illustrates the point. The genetics thing is a valid point. It is now thought that cancer is due to a defective anti cancer gene. Some people have a genetic predisposition, some don’t. What your doing though is playing the percentages game. Let’s take as example 1000 smokers, all smoke 20 a day. All other lifestyle factors are normalised. 10% die in accidents. 20% of them die before 50 due to smoking related diseases, another 30% before 70, another 30% before 80, bit 10% grow old and die of something unrelated to smoking. They all took the same risks but because of their genetic predisposition the effect of their lifestyle choices has a different effect. Sure, you can go through life smoking 20 a day and live until you’re 98, bit you’re loading the probability dice against yourself. If your overweight, have a bad diet, work shifts, have a stressful job and drink too much then you load the dice up more. Interestingly research done on Egyptian mummies showed no evidence of cancerous changes even on old age, ancwr appears to be a fairly modern phenomenon. Disclaimer - before anyone asks me to evidence those figures I made them up to illustrate the point!