You're duty is to protect your child, and put his health, safety, and well-being above you're husband's superficial, selfish desires or baseless fears. If he won't discuss it and is not open to research or reason, he doesn't deserve to have any say in the decision at all, because that's simply not responsible or loving parenting.
You're child's genital integrity is his birthright
, just like his arms, legs, fingers, toes, eyes, ears, earlobes, nose...Amputative, cosmetic surgery on a non-consenting minor without a medical indication is a violation of his basic human rights. It need not even be put on the table for discussion. As our dear Frank always says, our children's genitals are not a bargaining chip.
Do you see circumcision as unnecessary, painful, and damaging? Is it an abuse...of his human rights, and your authority as parents? If so, can you imagine another situation where you would allow your child to be irreversibly harmed in order to preserve a romantic relationship?
Consider how you will feel if you allow this to happen, by supressing your protective maternal instincts and allowing him to do this to your son merely because they are the same gender. Realistically, who's going to be changing the dressing on his wounds? Who's going to be changing the majority of diapers and giving most of the baths? Who's going to be faced with seeing his surgically altered, exposed penis every single day, multiple times per day, for at least the first few years of you're son's life? You.
The guilt and resentment giving in to his demands and failing to protect your child may breed will likely have a far more negative effect on your relationship than putting your foot down and saying "No." to cosmetic, genital reduction surgery on your healthy baby boy.
Please don't assume that you're signature will necessarily be required for him to have it done. Some men will go behind their partner's back and have a circumcision performed against her wishes. It has happened. If you refuse, and he's still adamant and threatening to do it anyway you will have to be dilligent in keeping your son with you at all times and might wisely consider a protective order or some other sort of legal action (contact arclaw.org) to restrain him from having it done without your consent.
It's ideal of course to reach a mutual conclusion of protecting your son from unnecessary pain, loss, and harm by keeping his body and choices intact. However, if this becomes impossible I implore you to protect your son at all costs, no matter what. He's depending on you, and sacrificing his foreskin to maintain your marriage is not a reasonable or ethical price; it doesn't belong to either of you.
Please also read through the circumcision regret thread
Positive thoughts, courage, and perseverance to you...