Okay, so the smoking/not smoking debate isn't usually an issue at the forefront of the whole green mentality. The general viewpoint seems to be that smoking is bad for your health, and people that care about the environment usually also care about themselves, so they don't do it. Easy enough.
Additionally, smoking causes air pollution (contained, perhaps, but it does ruin air quality in an area where there are a lot of smokers) and the cigarette butts tend to end up on the ground as often as in landfills, neither of which is eco-friendly.
But I have to say- smoking has another side effect that I hadn't been aware of until I started getting essays from my students this semester- if you smoke in your house, and print your essay on paper from your house, your essay will reek of smoke. It's absoutely horrid and makes me feel as if the paper has been polluted. I feel bad for those that will end up coming across it during the recycling process.