I do suffer from asthma, and cigarette smoke does aggravate it. The transition from smoking-allowed to smoke-free was wonderful for me.
But that's not why I asked the question. Over the years I've found that people who argue as you do -- demanding "direct evidence," and all that -- tend to be smokers. I figured, based on your responses, that you must be a smoker, and I was correct.
Now, we need not know the exact cause of death to know that smoking has a very significant effect on life expectancy. The difference between smokers and non-smokers is several years (see, e.g., here, search for "smoke").
As for ETS, it's been shown to aggravate existing conditions in children, such as asthma, and some studies like this one claim to have found that ETS is a significant factor in the development of asthma.
The point, again, is that significant exposure to ETS does have negative effects on some people, even if the exact mechanism is not specifically known.
Nobody disagrees with the statement that smoking shortens one's life. Smoking a pack a day for 40 years cuts off several years.
For this analysis, let's say 5 years, or 1825 days. Now, SHS is breathed at a concentration about 1/1000, or less, of what the original smoker gets. That means someone exposed to SHS continuously for 40 years will have his/her life shortened by 1.8 days. Get it?
Further, over 50% of people over 85 suffer from Altzeimers. So, if your family history estimates your lifespan to be 90 without smoking, and 85 with, then you would do well to visit the Altzeimers wing of a local nursing home, to see if you think those 5 years are worth anything.
And, no, I am not a smoker. But I also know that it is not "addictive", because I quit approximately 35 years ago.
IN that case, could you please explain why with a lot fewer smokers, asthma cases are skyrocketing. ??