It's not your fault. It is hard to make sense of half-truths,
junk science and propaganda.

Tobacco is protective against the toxic effects of mercury
on brain, such as those found in Alzheimer's and Parkinson's
diseases. Smokers at any age have less than half the rates of
these diseases than non-smokers. The smokers who quit double
after few years their odds for getting these diseases, nearly
catching up to never-smokers. Further, the brains of Alzheimer's
patients show significant excess of mercury. In test tube the
mercury in similar or lower concentration than those commonly
found in brains of people with amalgams and who carry single
or double ApoE4 allele, produces the same tangles on neurons
as those characteristic of Alzheimer's disease (mercury is the
only known substance so far that produces such effect on neurons).

http://www.fda.gov/ohrms/dockets/dailys/02/Sep02/091602/80027dd5.pdf
http://www.altcorp.com/DentalInformation/alzheimers.htm

Note also that almost all longevity record holders, such as
those above 110 and still mentally sharp, are life long smokers.
Here are some links and summaries of little publicized studies
and facts on smoking and anti-smoking:

  "The Scientific Scandal of Antismoking"
  http://members.iinet.com.au/~ray/TSSOASb.html

  "In defense of Smokers" (online book)
  http://www.lcolby.com/

  Some studies on therapeutic effects of smoking:

  http://www.forces.org/evidence/evid/therap.htm
  http://www.data-yard.net/10/nicoplus.htm
  http://www.forces.org/evidence/evid/life.htm
  http://www.forces.org/evidence/hamilton/other/oldest.htm
  http://www.forces.org/evidence/hamilton/other/nicotine.htm
  http://speakeasyforum.com/eve/forums/a/tpc/f/173601742/m/7541044041

Of course, there is a statistical _correlation_ between smoking
and poor health (as well as with variety of other problems). Much
of it, perhaps all, is the result of strong social pressures against
smoking which have reshaped the population of smokers in recent
decades, turning smoking into a mere passive marker of various
negative traits statistically associated with that highly skewed
sample (e.g. risk takers, low socioeconomic status, unhealthy &
stressful job environment,... ). As demonstrated in the studies
cited & described at the first link above, large controlled
experiments spanning decades, in which subjects are randomly
assigned to either smoking cessation or to no intervention group,
showed no gain, and even increase in some diseases, for the
smoking cessation group. Similarly, the studies examining health
problems of smokers and non-smokers in otherwise fairly
homogeneous groups, such as lung cancers among asbestos workers,
have found that lung cancers were much more prevalent among
the non-smoking workers. Curiosly, among smokers in general, the
lung cancers are also significantly more prevalent among those
who do _not_ inhale the smoke than those who do inhale.

------ quoting from ----------------------------

"The Scientific Scandal of Antismoking"
http://members.iinet.com.au/~ray/TSSOASb.html
------------------------------------------------

By the end of the century general opinion had changed. The Royal College
of Physicians of London promoted smoking for its benefits to health and
advised which brands were best. Smoking was compulsory in schools. An
Eton schoolboy later recalled that "he was never whipped so much in his
life as he was one morning for not smoking". As recently as 1942 Price’s
textbook of medicine recommended smoking to relieve asthma.

These strong opinions for and against smoking were not supported by much
evidence either way until 1950 when Richard Doll and Bradford Hill
showed that smokers seemed more likely to develop lung cancer. A
campaign was begun to limit smoking. But Sir Ronald Fisher, arguably the
greatest statistician of the 20th century, had noticed a bizarre anomaly
in their results. Doll and Hill had asked their subjects if they
inhaled. Fisher showed that men who inhaled were significantly less
likely to develop lung cancer than non-inhalers. As Fisher said, "even
equality would be a fair knock-out for the theory that smoke in the lung
causes cancer."

Doll and Hill decided to follow their preliminary work with a much
larger and protracted study. British doctors were asked to take part as
subjects. 40.000 volunteered and 20,000 refused. The relative health of
smokers, nonsmokers and particularly ex-smokers would be compared over
the course of future years. In this trial smokers would no longer be
asked whether they inhaled, in spite of the earlier result. Fisher
commented: "I suppose the subject of inhaling had become distasteful to
the research workers, and they just wanted to hear as little about
inhaling as possible". And: "Should not these workers have let the world
know not only that they had discovered the cause of lung cancer
(cigarettes) but also that they had discovered the means of its
prevention (inhaling cigarette smoke)? How had the MRC [Medical Research
Council] the heart to withhold this information from the thousands who
would otherwise die of lung cancer?"

Five year’s later, in 1964, Doll and Hill responded to this damning
criticism. They did not explain why they had withdrawn the question
about inhaling. Instead they complained that Fisher had not examined
their more recent results but they agreed their results were mystifying.
Fisher had died 2 years earlier and could not reply.

This refusal to consider conflicting evidence is the negation of the
scientific method. It has been the hallmark of fifty years of
antismoking propaganda and what with good reason may well be described
as one of the greatest scandals in 500 years of modern science.

-------- end quote

These anti-tobacco social pressures and the resulting mass
hysteria being whipped up in recent decades are not accidental.
Hundreds of billions are being transferred every year from the
pockets of smokers to the pockets of those creating and financing
all the "grass roots "antismoking organizations and buying the
junk science and politicians in the support of their extortion
racket. For example, of $60 per carton of cigarettes in my state
(MA), $15 goes to the Big Tobacco, tobacco farmers and all the
sales and marketing. The remaining $45 goes to the Big Anti-tobacco.
Some links with more details on the money trail are here:

http://cleanairquality.blogspot.com/2006/08/its-time-for-full-scale-congressiona
l.html
http://www.forces.org/writers/kjono/pdf/tobacco_control_and_fda_regulation.pdf