Firstly, the question was about vaccine passports, not negative test passports. But that is an even more idiotic suggestion. Not only do you still have to have staff checking and verifying passports/certificates prior to permitting entry, which is wholly impractical, but anyone not yet vaccinated would have to get a test every week/10 days. That's just not feasible IMO. But if we insist on going down this dangerous road, why stop at pubs? Why not extend it to every public place, including shops, so you literally cannot go anywhere without proving you are "clean"?
It's dangerous to even contemplate starting down a path of state sponsored segregation that discriminates against half the population, primarily based on age. If that happens, I'll be right behind the millions of young adults that will surely rebel against such draconian measures that deny them the same privileges that those lucky enough to have been vaccinated are selfishly demanding for themselves.