None. But you said that driving is a privilege, not a right, and I can be stopped any time for a DUI test because I agreed to that when I got my license. I simply asked you, since it is a privilege, if the gov't said, well, to get a license you must agree to be stopped any time for a DNA test, would you be ok with that?
After all, as you say, driving is just a privilege and the gov't can attach conditions to it, so why not that condition?
No, because such a stop would have no valid reason. A stop for DUI occurs when you are visibly incapable of safely operating the vehicle. The field sobriety check and BAC are supporting evidence for the observed unsafe driving behavior.
States have seat belt laws too. In Idaho, that doesn't constitute PC for a stop. It can only be considered if a stop occurred for another valid reason.