"...It is so much nicer in Vietnam where I can board with the PDF in my confirmation email, and I don't have to go through security, and in general can plan to get to the station 20 or 30 minute buffer, and simply walk to the platform when the train arrive..." - yes, it is fast to get on the train but very slow to get you to your destination.
Like it or not, security is here to stay. It is what it is, you just have to live with it.
And I don't take off my shoes at US airports.