To be clear, are you saying that you find it to be a seizure (thus necessitating reasonable suspicion) because it is a means of generating evidence of a crime?
If that's what you're arguing, then ethically speaking you could probably sell me on it. I hadn't really considered the matter outside specifically constitutional bounds. And I'm not familiar with any constitutional correlation between (A) the distinction between seizure and voluntary lawful contact, and (B) law enforcement obtaining incriminating evidence.
I guess the thrust of my argument, which I believe would strike your above comparatives, is that driving into a checkpoint is a voluntary act on the part of the motorist. The checkpoint is there, and you'd know it long before you get there - enter at your own risk, fully aware of the consequences.
This is as opposed to a policeman showing up at 1:45 outside a bar and issuing citations, where essentially a trap is set, or a search of your home (7960's comparison) where you have (I assume?) an unprovoked invasion of privacy, initiated by law enforcement.