First and foremost, mazel tov on your growing family!
You and your spouse are in charge of your nuclear family, and joint decisions should absolutely be taken seriously by your parents. Together you can choose to not raise your son Jewish, and you can choose not to be Jewish yourself – free individuals in a free country can make free choices. But “Jewish” can mean many things, not just how you were raised or what your parents think.
Your new family life could be just like your wedding: “the fun Jewish traditions” you enjoy without religious obligations and restrictions you reject. You can spin dreidels on Hanukkah, cheer Mordecai on Purim, or sing along with Fiddler on the Roof whether or not you hold a bris, keep kosher, or even believe in a god. That’s the beauty of connecting to Judaism as family culture, as do Secular Humanistic Jews – it isn’t all or nothing when you choose the best of your heritage consistent with your values and lifestyle.
It’s not all or nothing, and it needn’t be either/or: bris or nothing, Jewish religiously or not Jewish at all. Today many intercultural parents separate surgery from celebration: they choose creative baby welcoming ceremonies that are gender neutral and can honor both sides of the family. Children can participate in both the Jewish culture of your family and your spouse’s unique cultural/religious heritage. If you are concerned that “being Jewish” is an implicit rejection of your son’s other grandparents (or his father!), please know that your family and your son will be lovingly connected to more than one family of origin. You are on both family trees, and your son can have roots in both family cultures. Even if you want to be nothing, your children may well want to know where they came from.
You may still choose to disconnect entirely from Judaism. And your parents will need to listen, for this and for other choices. But absolute declarations at this stage may not pan out. Having an actual child transformed my perspective on many issues: after the third consecutive night of a toddler awake at 3am, you re-evaluate the benefits of bribery! As your son grows, you may decide that you want to see his face in the light of Hanukkah candles. And you can, no matter what you do when he is born.
Adam Chalom is the rabbi of https://kolhadash.com/ in north suburban Chicago and Dean for North America of the International Institute for Secular Humanistic Judaismhttp://www.iishj.org/.