YANBU at all.
One of DH's best friends got married in his bride's hometown which was a 5 hour drive away and necessitated two night's staying over. They had a no children rule due to budget.
When he explained that to me, I said, no problem at all, completely understand, but I would have to sit it out - since DD was 4 months old at the time, and EBF. I couldn't leave a bottle-refuser who was used to me being around all the time, for 2 nights for anyone.
In the end, they said they could make an exception for an EBF baby under the circumstances which was lovely, but had they decided the rule was hard-and-fast, then fair enough, I'd have stayed home. Their wedding, their choice. We left DS with a babysitter for two nights and took DD with us.
Our wedding was child-free, except for a breastfed baby.
Fair enough if having a wedding with lots of children is your preference - and I can absolutely see the appeal assuming the children aren't the type to run amok, and/or the parents aren't the hopeless, ineffective types. I've been to weddings with kids present, and they've been great. Everyone's had a ball. Fab all round.
However, why can't other people see that child-free weddings can be great craic, too? A proper grown-up knees-up, gathering together people who love a good night out is brilliant. Both scenarios are great - so why not just go with what the B&G want, rather than coming over all sanctimonious with the 'legal and religious commitment' comments? With all due respect, Startail - your stance, while very worthy I'm sure, isn't go to persuade the childfree-types to your way of thinking, at all!