While the argument rages with ridiculous extremes on both sides (for the record, I don't think anyone thinks that children should be allowed to do whatever the hell they want in a public space, nor do I think anyone thinks that children should never speak above a whisper, but that seems to be what both sides are accusing each other of), a few very important points were made. The main one being competing needs.
Jackie commented that she experiences sensitivity to noise, and kids being loud are really quite unbearable for her. I have a kid who is still really struggling to control his impulses, and is well known for loud, frustrated outbursts. How would I handle it if Jackie (or someone with similar sound sensitivity - it ain't that uncommon) were a friend, or just someone who regularly shares the same space? Well firstly, I'd explain to my kids that not everyone experiences sound the same way, so that at least they understood the situation. In the end, though, I'd really need to keep noisy kid(s) away from Jackie, through sensible negotiation and a bit of thought.
All good and well if I know who she is and where she might be. But what if I don't know who she is, but she's often at the same places? It seems that the only real solution is that which has been implemented on some UK commuter trains - quiet spaces. It doesn't seem at all beyond the realms of plausibility that restaurants and cafes could choose to advertise as "Quiet" spaces, or reserve "Quiet" areas. We have cafes clearly designated as "loud" by virtue of having play equipment for kids, I'm sure you could do well opening the "quiet" one across the road.
This addresses a whole range of problems - the hens/bucks night at the table next to you when you were hoping for a quiet, romantic meal, the business meeting when you're trying to study and so on.
It also strikes me that parents would be a good group to advocate for such a thing - after all, when we do manage to escape the kids for a wee while, it'd be awesome to know there was a place we could go that was quiet. In addition, if the space is not designated as quiet, then we'd have better rules of engagement with the death starers and drive-by parenting suggesters.
I don't, of course, have any answers for the rest of the battle over there, except maybe downgrading the defensiveness. It seems like a lot of people have had so many bad experiences in way or another, they've given up believing that anyone is reasonable, which is a self-fulfilling prophecy.