Ugh! Checking ID at the ticket window does NOTHING, checking the ID at the platform does NOTHING, checking the ID on the train does NOTHING! I can forge an ID, I can get one illegally and worst of all even if it is real I could be a terrorist with a real ID.
The whole thing is a knee-jerk reaction to our fear that will eventually disasemble our society.
What does make sense (IMHO) is checking for ID when you purchase your tickets with a VISA card. I want to know that someone who just stole my card can't buy anything with it. That makes sense. If someone comes by my seat on a train in my country and asks for ID they're not accomplishing anything but giving themselves something to do. Does Amtrak bar foreign people from it's trains? Do they bar American citizens from it's trains? Do they keep a list of known terrorists with them and check everyone's IDs with the list? No on all accounts. Checking IDs on a train or before it leaves is a complete waste of time.
If they were actually concerned about security they'd scan the bags and check the ID in a computer system with a DO NOT RIDE list. Anything short of that they're wasting our time. Let's not forget Timothy McVeigh was an American with a valid ID and could have ridden a train anywhere he wanted.
Grant