First, let's review the circumstances of this case.
There was a man who *had done nothing wrong and there was no actual reason to take him to jail*. He had previously owed a fine and paid it; an error in the computer system showed there was an outstanding warrant for him when there wasn't. Further, he knew that - and they didn't fix it, so he carried in his car paperwork proving he had paid the fine, to show an officer if pulled over. The officer ignored this and took him in anyway, arresting him in front of his pregnant wife and 4 year old. He spent six days in jail.
It's not relevant to the issue, but good background info. Oh by the way guess his race.
As for the legal issue - it's an interesting question. There is something to be said for erring on the side of security in jails.
The chance of a person randomly arrested for a minor crime having contraband in an orifice is all but zero. The chance for anyone arrested by surprise is all but zero, other than someone specifically arrested for suspicion of trafficking by concealing in an orifice. But something that hasn't been mentioned yet:
I've heard from a former young women who had been in jail that it was a lot easier to get drugs in jail - whenever you want - than on the outside. I was dubious about the claim - such people aren't the most credible - but I asked an ADA about the claim and was told they could easily believe it. There's plenty of anecdotal evidence of drugs in jail.
Now, what if a gang associate wanting to smuggle drugs into a jail knew they could store them where our right-wingers store their political views, and then intentionally get himself arrested for a minor charge - and expect he'd be processed into contact with the general population without a strip search? Could that not only happen but already be happening?
It's worth thinking about. Unfortunately, while it's clear this searching in this case was not 'reasonable' in terms of risk, it's hard to put the distinction into law.
I remember old movies where someone arrested by not be 'degraded' by the Sheriff by being put in handcuffs when taken in - those times are gone.
The days of respect of 'dignity' to the point of things like that are gone - in part because some people abuse the better treatment.
Remember the court here isn't deciding 'what's the right treatment', but 'does the constitutional prohibit the government from the widespread strip searching'.
The Supreme Court isn't likely to prohibit the government from spending $10 billion to prove the earth is flat - the barrier to that is the political process, not the legal one.
I haven't reached a firm position on this, as much as I can hardly think of any issue where I'd agree with the 'radical right 5' over the 'moderate 4'.
Something to think about, though, about why there's some basis for this ruling.