I agree that there are serious health effects from smoking cigarettes, cigars, hookahs, etc., but those aren't the direct reason for the bans.
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I also find tobacco smoke unpleasant and believe that health dangers of secondhand smoke are real.
Those are the real reasons why it's banned in public places. Smoking does not just hurt yourself (that's mostly your problem, who cares) but also the people around you.
Alcohol is banned from traffic for exactly that reason, too. Nobody cares if you drink and drive and end up dead on the next tree1. On the contrary, that's one more organ donor, and we need organs, so you're actually doing something for society. But the problem is, you risk running over a pedestrian or hitting another car (or think a bus with 20 people) and kill non-drinkers.
What if... where to draw the line?
The line is drawn by insurance companies, or in the case of public health insurance, by the government. It needs not always be perfectly logical, but there is some logic behind it. In the case of insurance companies, they simply count the number of incidences during the last 20 years, round up to the next ten percent, and calculate your fees from that. Then they multiply the result with 1.5.
There is an important difference to note. Drinking can kill you, but moderate drinking will usually not have that effect. Eating sugar can cause diabetes, but needs not, and in moderate doses will not. On the other hand, the effects of smoking are, although denied by the tobacco industry for obvious reasons, undeniably always desastrous. There is no threshold, no harmless dose, and there is no beneficial dose either.
Given enough time, nature makes the best out of most toxic/harmful things, or at the very least it finds a way to mitigate the adverse effects (Why? well simply because the ones who can't cope die early!). Sunlight is extremely harmful, as is oxygen. We have dedicated systems that repair the DNA damage done by UV radiation and oxygen, and our skins have a built-in adaptive sunshield. Oxygen is the main component in our energy supply (and a waste product generated by plants, to whom the dangerous UV radiation is the main source of energy). Alcohol is quite harmful, but we have dedicated enzymes that not only disable the toxic substance, but turn it into a form of energy that our cells can use.
Now... nicotine... is a strong neurotoxin, so strong you can consider it chemical warfare. It's nature's form of sarin (well, not really... sarin inhibits the cholinesterase while nicotin directly binds to the cholin receptor -- but in essence it's the same thing). Nicotine serves one purpose for the plant: animals who eat the plant perish. But before you go into discussing at what dose the effects of nicotine may or may not become unhealthy, one should note that the other ingredients of smoke are even worse than the plant poison. Ultra small particule matter that cannot be digested by phagocytes, tar, and non-neglegible amounts of toxic and cancerogeous gases. Including an amount of CO which is so high that you can measure it in blood samples (and thanks to its high affinity, you can still find it the next day, so only smoking every other day is already enough to guarantee a permanent sub-par oxygen supply in organs).
So far, nature's best defense against smoke is that it causes you to caugh and flee from it (at least animals do that, humans sometimes seem to evolve backwards).
One of the biggest problems is that you cannot define a threshold for cancerogenous chemicals. Which is why for example that stupid "Oh, but you have to drink 1000 liters per day" quote which came up with the glyphosate beer story. The point isn't that glyphosate is kinda toxic (it is, too). The point is that it's actively damaging DNA (that is what it's made for, being a weed killer), and thus being a cancerogen and probably a teratogen, too. Sure, you can, and for economic reasons this is done, draw a threshold which is above what you've measured and yell: "Harmless, harmless, harmless!" all day. But that isn't what reality looks like. There is no "harmless" level.
About sugar and obesity, by the way, our Greens are trying to get a sugar tax going. Which is, of course, like all Green ideas total bollocks because the average person has no way of escaping sugar anyway, and it's in virtually everything you buy. If you are being honest (counting starch as sugar) that would be a tax on everything you can buy in the supermarket (except carrots and tomatoes). Thanks to the USA, notably the Nixon administration, there are huge amounts of corn starch in virtually every food. There's particularly high amounts of corn starch in "low fat" and "fit" and "healthy" products, too. Think Philadelphia.
There is of course a huge economic interest in that, too. A lobby ten or twenty times the size of the tobacco lobby (and that's not counting in the pharma lobby which has an obvious interest in people becoming diabetic). So... nothing will come out of that. Nothing useful or sensible, anyway. It will only make everything more expensive. Seeing how the Greens are ultra-left, that's an awesome thing to do, since it's only the poor who will feel food getting more expensive.
1Unless it's a protected tree, or one of a partiuclarly precious kind.