Making it legally dodgy to dangerous in mainland europe, either way certainly not reliably licensed.
However if me and my company and everything is in Europe and I use/redistribute the code in Europe I must follow applicable European law. If that doesn't accept that form of public domain the author (rights owner) could sue me and it were upon the judge, who sensible they are. (This is mostly theoretical - if the author decides to put it in public domain per U.S. law they most likely don't want to restrict to U.S.)
For an example see the recent case about project Gutenberg https://news.ycombinator.com/item?id=16511038
Generally speaking, the risk is less the author themselves (though they could always do an about-face for whatever reason, it's hardly unprecedented[0]) and more eventual heirs of them who could always decide to cash in.
[0] https://en.wikipedia.org/wiki/Alexander_Grothendieck#Retirem...
But if this really concerns you, I would be happy to provide you -- or anyone else -- with a licensed copy of any of DJB's code for a modest processing fee.
Well, I've come across companies that have policies against using unlicensed or public domain code.
This sadly makes whether it's a founded concern irrelevant, as the licensing choice suddenly prevents me from using the code in any shape or form if I work there.
In the US. Public domain dedications have no legal standing in most of mainland Europe's IP regimes. A public domain dedication is the equivalent of no license at all.
And because a public domain dedication has no legal standing, a third-party slapping a license on the code does not make it legally licensed as far as european IP courts are concerned, they don't have that right, their "license" is worth as much as you deciding to license Windows under GPLv3.
> But if you think you need it licensed, you can have it licensed.
Unless djb offers to provide a fallback license (which incidentally is exactly what CC0 does and why it's legally sensible and valid[0]), then no, you can't "have it licensed".
[0] https://rd-alliance.org/sites/default/files/cc0-analysis-kre...
"It is worth noting that the result would stay the same if CC0 would not even contain such an explicit fallback rule. According to the prevailing opinion of the legal scholars, public domain licenses (which cannot be interpreted as a waiver of rights under the German copyright, see above) are reinterpreted as unconditional, unlimited, non-exclusive (i.e. public) licenses."
which appears to contradict your statement that public domain dedications are treated as no license at all.
