Hi, Scruffy, and congratulations on your upcoming happy event!
I want to offer a different perspective on this, but I don't know if I'm going to be able to explain it very clearly, so bear with me. What I want to share is a lesson I've learned over nine years of marriage.
What I've learned is that when DH feels really strongly about something and I disagree, framing it as "I'm right and he's wrong, so I'll back myself up by listing all the reasons why I'm right" actually doesn't work very well for solving anything. Sure, it might 'work' in terms of bolstering me in my position to the point where I can stick to my guns and override his objections... but the end result isn't just that I get my way. It's also that his feelings get hurt because I wasn't prepared to think about the issue from his point of view or acknowledge the fact that he also has strong reasons for feeling the way he does. I've been in situations like that where I've looked back and thought that actually, in retrospect, the price of getting my way was too high in terms of the bad feeling it left between us.
Now, that isn't to say that I need to just flip things around and give in every time. It's to say that I've learned it's actually better to take a different approach from the start - to acknowledge his feelings and reasons as well as mine, and to see whether we can discuss these and take them both into account. For a while, I got into the habit of asking myself one question whenever we disagreed: "How do I *know* it's him and not me who's wrong?" I don't actually ask myself that question any more, because, of course, it's still too simplistic - often it's not a case of either of us being wrong (as is the case for you here) but simply both of us feeling differently, but still legitimately, about an issue. But I still think it's a good question for getting some perspective on a disagreement. ;-)
I don't know if you've read any positive discipline books such as 'How To Talk So Kids Will Listen And Listen So Kids Will Talk' or anything similar that goes through the process of coaching your children through conflict resolution - maybe that all seems way too far away at the moment - but there is a basic procedure. You acknowledge the other person's viewpoint, then you state yours, and then you see whether the two of you can brainstorm solutions that will deal with both sets of concerns. **In that order**. Because, no matter how strongly you feel and how important it is to you to tell the other person all the reasons why you're justified in feeling that way, the discussion is actally going to go a lot better all round if you start with acknowledging where the other person is coming from.
So, instead of opening this discussion by telling him all the reasons why you're not going to do what he wants... open it by acknowledging that this matters to him, by letting him know that what matters to him matters to you, and by asking him more about why it feels so strongly about him and listening to what *his* reasons are for wanting this. And set your feelings aside for just a few minutes, while you hear his point of view on the matter and let him feel heard. After all, isn't that what you'd want him to do for you if he disagreed with something you wanted?
Once you really get where he's coming from and why he's coming from there, and he knows you really get it, *then* it's fine to bring up your concerns. But, if you've heard more about what he wants and why, you )as in 'both of you working together to solve the problem') will be in a much better position to find a compromise that suits you. Alternatively, maybe there just won't be a mutually acceptable solution here and maybe the two of you are going to have to accept this as one of life's insolubilities. That happens. Maybe this will still end with you having to put your foot down and say, sorry, this just isn't negotiable for me. But, even though that outcome still ends up with him being disappointed... at least he'll know that you took the trouble to hear him out and that his feelings were important enough to you for you to listen to him and try hard to find a solution that was satisfactory to him as well as to you. And, believe me, that'll leave the issue as a lot less of a sore spot between you.
Good luck, and I hope the two of you manage to work this disagreement out.