Why, if you're in a pub in Britain, and you don't want to get drunk, are you supposed to drink litres of sugar? Fizzy drinks are like that, but also so are the fruit-juice based things like J2O - waaaay sweeter than beer or wine. What should pubs serve? There are loads of options!
Apfelschorle. Common in Germany, this is apple juice mixed with fizzy mineral water. I had this in Germany and I noticed what a good drop-in replacement it is for beer. It's nowhere near as sweet as fruit juice, and has some of the same refreshing fizzy clarity of lager. Obvs it's nowhere near the same as lager but still a great drink for when you don't want to drink.
Iced tea. Even if it's simply bottles of Lipton Ice that'd be OK. But, as is common in some parts of the USA, it'd be great to brew up a nice big vat of fresh iced tea each day, especially on hot days. Tea is very very cheap to brew up so pubs should be able to do a good markup on it.
Club Mate. It's a sort of not-too-sweet soft drink made from "mate" and allegedly popularised by the Chaos Computer Club or something. Just like the other suggestions, it's got a beer-like bitterness and is unsweet enough that you can drink it in pints.
Kombucha? The Guardian seems to think it's starting to be served
Alcohol-free beer...! well OK this is obvious enough - most alcohol-free beers taste a bit odd, of course. My favourites are Brewdog's "Nanny State" and Claustenhaler's alcohol-free lager, the latter being very convincing German lager. ... But then, now that I've written down the arguments in favour of apfelschorle and iced tea, I'm starting to wonder why we're buying more of these expensive alcohol-free beers. Maybe we're missing a trick.
What strikes me is that the branded bottled options are of course the ones that get promotional effort, yet almost all pubs could easily set up with home made iced tea or home made apfleschorle with very little overhead.