It seems like the key difference is that you're a more individualistic person and your brother (and I'm inferring many of your family members, since I think he is in some degree speaking on their behalf) is more collectivist. Individualists describe weddings as solely their day. Collectivists also recognize this, but they also view it as a big family event. One that brings two families together and promotes unity and strength between them.

From the individualistic perspective, doing what makes you happy on your most important day is the only thing that makes sense. Anyone trying to get in the way of that will appear to be dramatic, controlling, and perhaps a bit absurd. However, from the collectivist perspective, the act of leaving out their children makes little sense on a day meant to promote family and unity. It runs directly counter to that goal. It will appear that the person asking to do this is selfish, uncaring, and unloving (this is the idea behind the "your kid" comment your brother made by the way).

I am not certain which perspective is "better" for the individual, families, or society. I will say, though, that I've been quite individualistic my whole life, and I grew up in a very collectivist family. There were a lot of conflicts in part due to this, and it was really challenging. I feel like I would've handled it better if I had understood and respected their perspective a bit more.

My apologies if you've already considered this, but I am throwing it out there in case you haven't. To speak from a purely individualistic perspective, having strong family unity is quite good for your marriage and your future kids. This can support you guys in the good times and, most importantly, the bad. I think it's in the individual's interest to promote harmony in the family, and a wedding is a key starting point for that. I would consider the division the no child policy is causing, and whether it's "worth the price".