One of my biggest reasons for being so opposed to tobacco use is the way that smokers selfishly put their desire to smoke ahead of the health and safety of their children:
Perhaps the worst display of selfishness is smoking near children.  A child cannot leave to avoid the second hand smoke the way an adult could, and often are too young to understand the negative effects of second hand smoke.  It strikes me as particularly wrong for an adult who is supposed to love and care for a child to expose that child to the potential of death or great suffering, just because that adult wishes to smoke and is too lazy to go outside.  What makes this particularly wrong is the way that the child suffers these risks, but enjoys no benefits.  For example, a child who is a passenger in a car has a (relatively small) risk of dying in a car accident, but this risk is offset by the benefit of being transported to school or to the doctor or to a friend’s house.  But a child who is exposed to second hand smoke gains no such benefits.  It is the pinnacle of selfishness to expose children to second hand smoke, and to set a bad example for them that will increase the likelihood that they will smoke when they get older.

I’ve heard a variety of counter arguments to my above statements, none of which I’ve found to be persuasive.  First, some will say that smoking around children isn’t harmful.  This is simply untrue, as children are particularly vulnerable to second hand smoke.  Others will say that their parents smoke around them as children, so it is OK for them to smoke around their children.  This is also a flawed argument, as one (historic) wrong does not justify the (current) wrong.  Once upon a time, people didn’t get their children vaccinated and didn’t have prenatal care when pregnant, but a good parent these days will make sure that their children receive both of these modern benefits – and people didn’t fully appreciate the dangers of tobacco 50 years ago.  I’ve also heard smokers say that smoking around their children is nobody’s business but their own.  Just as a parent cannot claim that a right of privacy allows them to beat their children senseless or to starve them, nor can a parent use privacy to justify endangering their child with second hand smoke.