I should have been more clear in my comment, I was referring to international high speed trains. Including mandatory registration of passengers and keeping the data for X years. Presumably these passenger manifests are also exchanged with other countries.
But even regional services include oodles of cameras, including on the trains. There's tracking of passengers and their destination. There are heavily armed guards/police/soldiers in many European train stations.
Hmmm...those trains I step onto are (a) typically high speed and (b) quite often "international", though the concept really doesn't make much sense in the Schengen Area.
Are you talking about the Eurostar service from London (I remember the Waterloo station, though I hear it has moved to St. Pancras). That's the only one I can think of that fits your description.
The Thalys from Cologne to Paris via Belgium is/was also simple walk on walk off with normal train stations.
The Thalys has security theatre with luggage x-ray in several locations, including Paris and Antwerp. It's currently not active 24/7, but it will be soon.
On the TGV from Luxembourg to France, there were no barriers. And nobody ever asked me for my ID; in one of the legs, they didn't even check our tickets.
I don't doubt they keep those manifests, but I've found very little actual control.
Brussels does have troops going around, which is unsettling, but I never saw them inside the actual station, nor stopping people entering it, even after that poor devil immolated himself last year.
Curious. Is that very recent? I was in Amsterdam last year and while I remember the ticket validators, I don't remember them being mandatory; I think we've even passed them to cross the station to the other side, to catch the ferry.
Living in the UK, I've not really seen any invasive security, beyond a ticket turnstile at train stations, or anywhere in Europe. Is this a thing in the US?
I regularly travel to Peru. For years now, it has been the policy of the Peruvian aviation authority that you may not board flights to the US with bottles of water purchased after the security checkpoint.
They have queues set up at the gate to rifle through your knickers in search of contraband dihydrogen monoxide, and will force you to dump any you have, and/or deny you boarding if you don't comply obsequiously enough.
Flying to Mexico (or anywhere else) and then the States? Or even Europe? You're fine. Even when you board the flight that will land in the States, your water is welcome. It's only direct flights to the US, and it's only (in my experience) enforced on outbound flights, from Lima. I've never encountered this anywhere else, and I've visited dozens of countries, and did a several months long RTW a few years ago.
Once you've spent 6-10 hours in a can at cruising altitude, with only the occasional thimbleful of water a few times, because of this kind of invasive idiocy, you might have a broader perspective on how much of aviation security is theater.
EDIT: That's just one example of the absurdity I've encountered in my travels. Another: being told that my carry-on sized backpack was somehow a material threat to the plane I was trying to board, and that it needed to be checked in the hold.
What am I supposed to do there? Logic my way out of my paid fare? Into one of $country's TSA-alike's interrogation rooms?
This nonsense is endemic to air travel, over the last decade particularly, and it's only getting worse.
Istanbul is not exactly Europe, and from what I hear from US friends they get special treatment there. Someone (from the US) I know swapped planes in Istanbul and said never again.