actually, the product that comes from a vehicle's exhaust is not the same thing as the gasoline you pumped in. Cars dont give out gasoline fumes, its a completely changed (and deadlier) product. Contact with gasoline and oil over prolonged periods of time does give cancer.. its the same principle with first-hand smokers.
Second hand smoking however, is the equivalent of someone washing his hands in gasoline once every 2 months. Or of someone taking a whiff at a car's exhaust once a week.
Cigarretes give your hit of nicotine and all the other crap in it by actually BURNING to create the smoke you inhale. Now, next time you see a smoker, pay attention to his cigarrete, not the person giving it a blowjob. You will notice a significant amount of that smoke NOT going into the smoker's mouth, but rather into the non-smokers around him.
Also worthy of note, every time you inhale you breathe in about (if memory serves me right) 1 liter of air. You exhale the same amount. However, from that liter of air you inhaled, less than half of the "fresh air" you inhaled is actually absorbed by your lungs...the rest is exhaled along with CO2 from your body.
So puff that little cigarrete again, exhale the smoke. From that smoke, so will less than half of what you inhaled be absorbed by your lungs.
So you see, second hand smoking is the SAME as being a smoker yourself, the only difference is first hand smokers get a much more "pure" amount of smoke on their lungs (thus why they turn soot black), while second hand smokers get a diluted version of it, because the smoke spreads out with the air as it travels the distance between the smoker and yourself.
