Honestly, what I don't understand are the people that demonize smoking (I've only read the first page, by the way - I figured pages 2-5 were more likely than not just people bickering back and forth).
If you live at a high altitude, the background radiation can be as harmful to you as getting 100+ chest x-rays per year, or living a mile away from the Fukushima nuclear reactor sites post-"incident".
If you live in an urban area, you're "smoking" the equivalent of one cigarette for every 2 hours you spend outdoors, counting the carcinogens from vehicle exhaust, sewer grate exhaust, air conditioner exhaust/etc. If you live in a truly congested area (say, Los Angeles) with a lot of smog, that can go down to as much as the equivalent of 1 cigarette every 30-45 minutes. Passing by someone who is smoking at a building entrance or on a street sidewalk gives you roughly the same exposure to carcinogens as standing at a bus stop in that city and waiting for a bus.
If you eat food that's been exposed to pesticides, preservatives, or growth hormones, you're taking in roughly enough carcinogens to represent the LD50 (the amount of toxins necessary to kill 50% of the test population) of a moderately sized rat every week.
Also, an amusing anecdote.
I work in the healthcare profession. When a patient dies, we have to undergo what's called an "M&M conference", where a bunch of other doctors get together and we present the case, then we all put our heads together and try to figure out what happened, and whether or not we made any mistakes. One of the tools we use to do this is a death certificate filled out by a medical examiner, listing primary cause of death, secondary causes of death, and contributing causes of death.
I had a patient who was hit by a car, rupturing his spleen (among numerous other injuries), and he ended up bleeding out on the operating table while we tried to repair the damage caused by getting hit by a friggin car. On the death certificate, the ME noted that he found evidence of smoking, and listed it as a contributing cause of death.
This happens more than you'd think - anyone that comes onto an autopsy table with more than "normal" wear and tear on their lungs has smoking listed as a contributing cause of death, even if it quite obviously had absolutely nothing to do with it, like with the patient above who died as a direct result of getting hit by a car.
These statistics are what (almost) everyone uses when they try to prove that smoking is harmful to you - the number of people in whom smoking contributed to their COD. It's a direct result of researcher bias. The researchers aren't doing their research to discover anything, rather they're doing it to PROVE that their hypothesis was right.
Now, on to the whole "smoking causes cancer" argument.
If carcinogens actually caused cancer, then everyone would have cancer. Contributing to the CHANCE of getting something is entirely different than actually causing it. It's like, you pick numbers on a lottery ticket. Removing a few of the numbers you DIDN'T pick contributes to the chance of you winning the lottery, but it's not a guarantee.
There has yet to be a study that definitively proves a causal link between smoking and cancer. There are too many other variables to account for for any such study to ever be done, reputably.
As far as personal choice is concerned?
I can understand and wholeheartedly agree with people that say they don't like the smell of cigarettes, or the taste you get when kissing one. THAT is a valid argument. Everything else is just justification.
We as human beings like to think that there is a cause behind every random occurrence. We see something horrible, like cancer, and have to believe that there's some sort of cause behind it, when in fact it's simple random chance. The top two causes of cancer are completely beyond our control - that is, genetics and viral mutations caused by oncoviruses. Environmental carcinogens are a DISTANT third. If you ever got chickenpox as a child, or mononucleosis as a teenager, or you've ever had the flu, or a cold sore, you're at an increased risk of getting cancer.
Some actual numbers:
A twin study published in the New England Journal of Medicine showed that 42% of cancer risk is genetic in nature (in over 1,000 sets of twins, 42% of the twins studied got the same exact cancer as the other twin that had it) (source: http://www.fhi.no/dokumenter/356607961f.pdf )
A study in the September 2010 Journal of General Virology (full text: http://vir.sgmjournals.org/content/91/9/2176.full ) suggests that the generally accepted "20% of all cancers are caused virally" is lowballing the figure by quite a lot. It's already known that the gammaherpesvirus (chicken pox) and epstein-barr viruses (something that's present in nearly everyone and has the nickname "the cancer virus") cause about 1/5th of all cancers, because they leave behind fragments of viral DNA/RNA that's replicated in cancer cells. This study shows that there can be viruses that cause cancer yet leave no trace behind after they've been eradicated by the body's immune system. At least read the abstract, it's an interesting study with solid methodology.
And remember, folks: the "American Society" and "American Cancer Society" are lobbyist groups, and wholly uninterested in anything that disproves whatever rhetoric they're spouting at any given time.