I guess what I was getting at was that in their questioning US citizens, at the immigration checkpoint, in a substantially similar way as they do visitors,
they seem to be trying to create the impression, intentionally or otherwise, that they can deny you entry if you dont answer the questions.

They can't, but having said that, they can indeed ensure you get a secondary inspection.

What I'm trying to say I guess is that if they are going to refer X percent, or every nth pax to secondary, or an Ag inspection, then just do it, but dont subject every returning traveler to questions that have nothing to do with their right to re-enter their own country.