First off, I will not be critical of you for wanting her to quit smoking, or for not wanting more kids, or anything else you decide.
We all draw our own lines in the sand. Some lines are more complicated than others, some lines are more liberal and some lines are more conservative, but in the end it comes down to what you can live with......and can YOU live with the consequences of YOUR choices?
Unlike Grunt, I've only got 39 winters under my belt, but I was married at 22 - divorced by 24, and remarried in my 30's. I'm now happily married to the gal of my dreams, the mother of my 3 wonderful kids, and a woman who is fiercely independant.
It took me a long time to realize that in life, making decisions is all about deciding what is the most acceptable consequence for our actions. A simple example. Should I drive on the country roads to get home and enjoy the scenery? The country road is much slower and is dusty and bumpy and there is that one spot that often floods over. OR, should I take the freeway home. It's much faster, smoother and I get to see my kids sooner. The freeway however is more dangerous and is often stressful. ------- the choice you take is based on your willingness to accept the consequences weighed against the benefits.
So, if you don't want anymore kids - and that is your final answer -- then being honest with your girl is the honorable thing to do, but be ready to accept the consequences of her potentially leaving your relationship.
If her stopping smoking because "she said she was going to, and hasn't yet" is more important to you than the value of her being in your life, fair enough, but be ready to accept the consequences of her potentially leaving your relationship. Either way, your decisions are going to impact your future and, from a personal standpoint, I really hate to look back on my actions and wish that I had been more thoughtful and self-aware.
In either case, your relationship with yourself, and with your gal is either going to be strengthened from the debate, or it is going to bend and break. Hiding the truth from yourself, and your loved ones, sure doesn't seem to be a healthy approach to me, but I realize that it is more complicated than that as you are not only selecting a wife, but also a mother for your children, but for that reason alone (mother) I think you owe it to yourself and your family to be honest with yourself (first), then honest with your gal second (second).
As one of the other guys alluded to, it does seem to me that your focus on the smoking (or so I have inferred from your comments) is really hiding some other issue. I don't know you at all, I don't know how fate has touched your life, but the fact that you are reaching out for advice to friends (and strangers) on a website seems to indicate to me that you need to take a long hard soul-searching look at yourself.
Find your line, define it completely and then draw it in the sand, but remember that lines in the sand can be erased and easily moved....I encourage you to give yourself the opportunity to see the truth --- then take your stand for better or worse. And in the end, I think that if a person can be honest to themselves and have knowingly made an educated decision based on the consequences, then I think you could hold your head high and be proud that you made an informed and honest decision -- which does not mean you can avoid the consequence, but knowing you acted with honor is important. Which, IMHO, seems to happen less and less in this world.
My 2 cents, offered with respect,
J