Barriers at every station? Most of the UK is not London, you know. There are 2,570 stations in GB. Some of them see one passenger a day. Are you seriously suggesting installing barriers in every one of them, with a minimum of two staff on each shift (barrier staff get assaulted enough as it is, lone working is not an option)? A line local to me has ten stations. That would mean twenty staff on duty at any given time, instead of having one conductor covering the lot. And no, you can't just not staff the barriers because people will simply jump them or force their way through. Barriers can't deal with all types of ticket fraud anyway.
A driver saved someone's life a few weeks ago. The bloke was about to jump off of a viaduct and the driver grabbed him and pulled him back. Can a computer do that?
Can a computer respond to an alarm, call an ambulance, and keep the drunks from fighting while paramedics arrive and deal with a ketamine overdose?
Can a computer eject a pervert?
Can a computer provide advice and reassurance to passengers, especially nervous travellers? The ticketing system is far too complex, and often an expert is needed to advise on what would suit individual requirements. Not everyone is conversant with smart phones.
Can a computer ask people to remove their feet from the seats, stop playing loud music, and stop swearing in earshot of other passengers?
Can a computer recognise sheep on the line ahead?
Can a computer stay for an hour after the end of its shift to wait with an old man in the small hours of the morning when the replacement bus departed without him, while phoning Control to arrange a taxi?
Can a computer help an elderly passenger lift their suitcase on and off the train?
Can a computer disperse feral youths who are intimidating passengers at a station?
Can a computer fault-find, isolating systems where needed so that the train can get back to the depot without being stranded in the middle of nowhere awaiting a fitter?
Can a computer lock a toilet out of use when someone has vomited all over it, and phone ahead for a cleaner?
Can a computer recognise a trafficked person?
Can a computer brighten someone's day with a friendly face?
By the way, never mind a buffet car, some of the trains around here have hot food, freshly prepared by proper chefs. Much more civilised than having a cereal bar for breakfast. That's how long distance trains should be.