The problem with etiologially associating smoking tobacco with death is that it can't be simply demonstrated that a dose-effect relationship can be measured and all such associations must be studied at great length and subjected to rigorous control methodologies to arrive at a statistically significant cause-effect relationship.
Long-term studies clearly show that career-smoking is harmful to one's health but so are many other normal and daily acivities such as driving in bumper-to-bumper traffic or crossing a busy street.
What hasn't been shown is a clear and present danger to being exposed to ETS in ordinary living arrangements.
As I said, I am opposed to general bans on smoking by government because it amounts to another abridgement of free association among groups. Current bans prohibit a gathering of all-smoking patrons in any place where one or more of the participants is an employee; only an idiot would think that this would lead to an improvement of these people's health - they will continue to smoke even if elsewhere, singly or in casual groups, and the general welfare neither gains nor loses.
It is the overarching reach of the big hand of government to which I object.
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.