If you smoke and won't give it up.
Surely other than being stupid that is the only reason to persist with such a vile habit.
I smoked myself until five years ago and I will admit that I found the thought of a life without cigarettes terrifying. I tried to convince myself and those around me that I enjoyed smoking when the truth was that due to being addicted I hated the feeling of not smoking. Five years down the line I feel just like you do after a cigarette all the time.
As a former addict I can say that although you don't think it's that bad you do smell. Those you say it's not that bad are being polite or they are used to it. When your kids are at school it is likely that people will know you smoke just by being near them.
Also do you want to meet your future grandchildren? I've just left the home of someone who will never meet his and it is heartbreaking. He used to say that it helped him relax but now he tells me that his throat was so dry and agonisingly painful that he hasn't slept since Monday afternoon.
I'm aware that in being contentious with this post but why else would you carry on knowing all of these reasons and more?