Thank you for that follow up information. You're right in that this can affect the both of you deeply, particularly when it comes to making decisions about your children, family, friends, jobs, even seemingly unaffected areas like where you will travel, live, go to church, do in your spare time, work, etc.
While whether or not smoking in the car can become a big issue, depends upon whether or not either of you smokes. For example, if you don't smoke, and don't want him smoking in the car with the children, and he defies that request. Or if his friends are in the car and he allows them to smoke while the children are in the car. If neither of you smokes, it seems like an insignificant argument, nothing that should be detrimental to the relationship, but could possibly come into play sometime in the future.
When it comes to how your children should be raised, its very significant. If you cannot agree how the children will be raised then you may want to reconsider having children with him. My first suggestion would be for you both to sit down with a piece of paper and a pen, and make a list of the 20 most important things about raising children, your "must have" rules, what religion they will practice if any, how you will discipline, how you want to handle religion, school, extra curricular activities, their friends, your home, meals/diet, medical care, etc. Once you make the lists, then you can talk about areas in which you and him are willing to compromise and areas where you feel you have to be firm.
Many people don't do this. They meet, fall in love, and get married and its only when they already have a few children that they realize that they have totally different ideas on how their children should be raised. It can be a very scary moment and have serious, long-reaching consequences.
This does not mean that the two of you cannot/should not get married. The point of loving someone is also loving their differences. If we were exactly the same as the people we loved, we probably wouldn't love them as much. It's our differences that attract and intrigue us so much.
While these are things to think about and address, they don't have to mean the end of the relationship, as long as the two of you are willing to sit down and discuss future plans. Additionally, if the arguments remain on topic, and do not consist of an attempt to make it personal or hurt the other person, then they are far more healthy that arguments that include pettiness, name calling or saying things to specifically hurt the other person.
I welcome your thoughts...let me know if you want to talk more.