I don't know that it's always rude to take a kid to Chez Fancy, but I'd consider it rude if you (general) were using Chez Fancy as a "proving ground" for Jr's restaurant manners. I, too, remember it being a Big Deal to go to my first "grown up" restaurant, and I was expected to demonstrate a higher level of manners and quiet than I would at a family-friendly place. I expect the same from my children.
Exactly. It's not the presence of a child; it's the behavior. I don't see how the mere presence of a child who is dressed at the same level of formality as the adults and who is behaving at the same level of formality as the adults can change the atmosphere of a restaurant.
For me, as much as anything else (and others have made excellent points I totally agree with) its the unpredictability level of children. Specifically very young children. Sure anyone of any age can act out at any time, but the odds of a young child acting out (being loud, whiny, kicking their chair leg which reverberates across the floor to other people at other tables, etc) is much greater then the odds of an adults doing so at a fancy restaurant later in the evening. And just having those odds upped, increases a particular level of tension.
The presence or absense of children can change an environment a great deal. If I'm out with a group of friends, whether or not it's a fancy gathering, it's an adults only gathering and we can and do frequently discuss anything. When children are present, no matter how well behaved they are, the entire tone changes. We have to censor our conversations, we have to be mindful of what the children will pick up on and what they won't, where they are and if they're getting into anything they shouldn't be. Yes, it is the parent's responsibility, but when there's a kid around, I'm on alert. And yes, this was in a public place, the child brought along was the only child.
The place we all met up at was a pool bar, which was 21 only after 9PM, but I've also seen at this place a load of parents bring in their young children at 8:45 and pay for several hours of pool because it got their kids in the door. They weren't escorted out after 9PM, so I guess the 21 only after 9PM only applies to people who show up after 9PM. Or who actually take the time to follow the rules.
Also, there are serious time issues as well. In college I'd regularly do runs to WalMart at 3AM. Lots of people from our dorm would, it was fairly common. And without fail we'd see children from infants up to nine or ten years old running through the aisles, during the school year, on a Monday or Tuesday night. Now what I choose to do with myself as far as my sleep schedule is concerned is my own business, but personally I don't find it appropriate to have a six or seven year old running around at 3 in the morning while the parents do their shopping. And on a regular basis I'd hear the parents telling the kids that if they calmed down then they'd get a treat (candy, soda, juice box were some of the examples I heard) when they got home. Or they were given to them in the store.
I don't have kids, and I'm sorry if I sound like a horrible grump about this, but giving a six year old a full sized can of caffeinated soda at 3 in the morning while you're out shopping? No. Not in any way appropriate for the child to be in that situation. At all. Ever.