Is it a problem? I've not been on a train since February and Storm Ciara.
Mostly not, which is why alcohol bans tend to be quite targetted in which trains they apply to and which they are enforced on (Merseyrail and TfL excepted, but do you *really* need to drink alcohol on a short local journey with no toilets?)
WMT for instance officially "call time after 9" on all their trains but you won't see any enforcement out of Euston most nights (you might on a Saturday) because that isn't where the problems are.
You are making this up as you go along Bletchleyite.
Individuals need to take responsibility for their own behaviour and be held to account when it falls on the wrong side of the law. Alcohol is not the problem, it is people with anti-social attitudes and the ineffectiveness of law enforcement in dealing with these individuals.
Sometimes it's either not cost-effective or practical to enforce against individuals. To use another example, I would imagine that a professional motor racing driver can quite safely drive at say 50mph past a school in a well-maintained modern vehicle, or say 120mph on a motorway, because their reactions are pin-sharp and their concentration excellent. However, most people can't, even if they think they can, so driving past schools at 50mph is generally illegal, 30 or 20mph being more common limits.
The ideal would be to have a couple of BTP on every "vomit comet" or similar problem train to properly monitor the situation and prosecute for D&D as necessary - but who's paying?
Just as, going back to talking about PFs etc, the ideal would be that there were enough properly trained revenue guards or travelling ticket inspectors on every train to check everyone's ticket and sell them one if necessary, and trains would never be so overcrowded as to make that difficult or impossible (which is how things were in the North in the 1990s, to be fair, but that was on a background of very low usage in most places, and basically everything being a 2-car DMU and most trains loaded well below 50%). But that mostly doesn't work, so "buy before you board" policies are imposed instead, which are a nuisance if you're running late because your alarm didn't go off, your kids were spewing everywhere and you got a flat tyre on the way to the station, but it's easier to apply the same rule to everyone.
The purpose of a restaurant is to feed people so they should ban alcohol?
Restaurants are typically a bit of a crossover, particularly when you come to things like late-night curry houses, but in practice I'd expect plenty of behaviour that would be accepted in a pub would at least get you thrown out (or refused further service) in a restaurant.
