If the government mandated them, they would absolutely be illegal searches. The government is not entitled to check whether or not I have a document containing certain content (illegal or not) without probable cause and a warrant to suggest that I do have that document (and that it is illegal).
I'm carefully not alleging that this is illegal, because it's a third party doing it and it's not obvious that they are acting as the governments agent. Regardless of whether or not that solves the legal problem of unlawful searches, it does not solve the moral problem that we have a right to be free from unreasonable searches.
Replace "child porn" with "political posters" here. If you would have a problem with that search, I claim that you should have a problem with this search, because the there is no evidence that the person you are searching is committing a crime, and as a result the claim for this to be a morally valid search needs to not be about guilt (which would require probable cause first), but about it not being a prohibited search in the first place.
