I disagree, but you make an interesting case, particularly the highlighted protion. Though if you refuse the test they're going to give it to you anyway (blood test), and if you're sober you'll walk.
I think the most absolutely blatantly unconstitutional police procedure is "stop and frisk", the practice of patting down certain people for absolutely no reason at all. But that happened to a specific group that most people like us really don't care enough about to protest. But that was some seriously unconstitutional crap.
Here's my take on it: Barring exigent circumstances (Amber alerts and so forth), an officer needs some reason to pull you over. It could be something trivial like touching the white line, going 1 MPH over the limit, or having a blown license plate lamp; but there has to be some reason. If you're driving within the law, the vehicle has no equipment violations, and there are no exigencies, you're supposed to be left alone. There's no violation of law and no probable cause.
So if it's illegal to stop one vehicle without probable cause, then why is it legal to stop a hundred or a thousand vehicles without probable cause? Because maybe one of them
might have been drinking? I don't buy it.
As for "stop-and-frisk," it stretched
Terry v. Ohio past the breaking point because it pretty much ignored the requirement that the officer have a reasonable basis for suspicion. That's one of the reasons why Scheindlin ruled in
Floyd v. City of New York that NYPD's application of Terry was unconstitutional, not the practice itself. The other was that it lopsidedly targeted Black and Hispanic young men.
"Reasonable basis for suspicion" isn't quite the same as "probable cause," but at least it's something. With the roadblocks, there is no basis whatsoever for the stops. Yes, one can safely assume that in any group of drivers, some are over the legal BAC. But one can also assume that on any city block, some people have weed in their possession. That doesn't give the police the right to search every house for weed, and neither should it give them the right to block the road and stop traffic for miles because some unknown person
might have been drinking.
Thankfully, GPS with crowd-sourced live traffic has made getting stuck in those jams pretty much history. Even if the device or app maker doesn't actually label a jam as a roadblock, the stopped traffic is enough reason to seek another route irrespective of the cause.
Rich