It's completely normal to not have any sympathy for a person who destroys their health and the health of people around them, even if it's past the stage of a deliberate choice and is just an uncontrollable addiction. You still can feel pity for this person though, but this is the feeling with almost zero warmth inside it. This is how many psychologically healthy grownups who don't need to justify their own flaws with sympathy for other people having the same flaws operate. There's no feeling of "supremacy" in it, it's nothing but a fairly unbiased pattern of identification of the facts of reality around you without redundant emotions clouding your thinking.
At the same time, it's not fair to say that those who smoke uncontrollably or have other heavy addictions are stupid. Often times they start it when they're just not informed or mature enough, and at the point when they're able to make an informed choice it's already transformed into an addiction which is very difficult to overcome. The willpower is not always enough, often it's defined on the biochemical level in your brain, and in this case some people are much more vulnerable than others, that's not their fault. Especially if it's tied to serious mental health issues which make them especially prone to alcohol abuse, etc., like bipolar disorder or borderline personality disorder, both of which are widespread disorders many people around us silently suffer from without us knowing about it. Shaming such people for alcohol or nicotine abuse - this is what being stupid is.
That said, you're not obliged neither to have sympathy for a heavy smoker nor to not have it, just don't be an asshole.