There are a whole bunch of different arguments and points of view here. One theme that is current across a couple of them is behaviour.
As a parent of two I dont necessarily want to spend a lot of time with them in a pub but do want to enjoy some semblance of a social life and take advantage of pub gardens in better weather. My worrying about my son annoying others gets to near-heart-attack levels in any public place let alone pubs so I try not to inflict that on myself too often. I think we all agree that there is a parenting issue with making sure kids are well behaved in public places.
So that's one side of it; but there also seems to be an issue with the behaviour of adults too. Pubs and licenced premises aren't generally there to provide environments where you can drink yourself somewhere near to oblivion but are supposed to be pleasant social environments. It seems odd to me that this is put across by a few people as a reason for keeping kids out of pubs without a hint that 'loud, drunken, sweary' behaviour is anything like the real problem. Surely excluding kids just means you don't feel so guilty about acting like a plum? I imagine most parents wouldn't take their Torquils and Pollyannas to a pub after about 6pm and I'd hope most of the side-affects of higher alcohol consumption happen later than this.
I might sound a bit wholier-than-thou in that bit, sorry - my own drunken debauchery only ended a couple of years ago with the birth of my own kids.
There is also a problem with the blurring of boundaries between different types of social establishment now. Restaurants try to be bars, pubs try to be restaurants and so on. I hope people really don't expect kids to wait until puberty to expeience a meal out so if you have kids in restaurants and pubs pretending to be restaurants then the nature of the pub has changed and you are going to have more kids in pubs than when we were all kids.
But rest assured, you are extremely unlikely to find me clogging up your pub with my kids, and if you do you are more likely to be annoyed by the neurotic father reacting to every little thing than by my kids tugging on your G-Stars (or Levis for us older types).