I just think it's a little bit inappropriate, but I can't really articulate why I think that way.
Probably because there's nothing logical behind it. How is a baby going to be harmed by being at a guns how as long at they're not under foot or grabbing at dangerous things? How are the other attendees going to be harmed as long as the child isn't in a stroller, under foot, or grabbing onto things?
Perhaps there's a deep seated idea that a gun show is an exclusively male gathering where behavior that wouldn't be acceptable elsewhere somehow is acceptable there?
I don't know, but we have babies in chest and back carriers as well as kids and as long as they're not causing problems for others they're welcome.