Are you seriously trying to tell me that the chainsmoker standing next to me at the bus stop is causing less damage to me then the 300 pound guy eating a cheeseburger on the other side of me?
Consider this: Let's say a chain smoker, someone who smokes 10 cigarettes a day, has a fairly good chance of getting lung cancer after a lifetime of smoking. first, there is a filter in the actual cigarette. What gets past the filter, some tar and nicotine, can accumulate in the lungs. The largest bits become lodged in the alveoli and cannot be breathed out, acting as carcinogens. the nicotine also represses the action of the cilia in your windpipe from removing phlem/smoke gunk. and this is for a smoker, who takes a concentrated, direct drag from the cigarette.
When he breathes the smoke back out, the biggest pieces of crap are still in his lungs. Not only that, but it is already vastly dispersed in the air, reducing the concentration at least 3 fold. Also, you're not inhaling enough nicotine to disturb the cilia's removal action. So an occasional whiff of a portion of this dispersed cloud of 2nd-hand smoke (lets say 2 whiffs every 3 days), even over a lifetime, obviously results in debatable health effects that become very difficult to relate to any hardcore evidence, esp considering everyone's exposure to 2nd-hand smoke vastly differs
