Given a legal dispute between informed developer and a copyright lawyer, caution indicates that I should pay attention to the lawyer.
As Bernstein indicates, Lawrence Rosen argues the other side of this. There is binding precedent on the question in the 9th circuit. However that precedent is not necessarily binding on other courts, the statute does not provide for such a mechanism, and we've already seen statutes bring works back under copyright which had been out of copyright. The most famous example being It's a Wonderful Life. Therefore it is possible that other courts could decide differently, and it is possible that future copyright legislation or treaties could alter the legal status of works that have been abandoned to the public domain.
And this is just the situation in the USA. There are about 200 countries in the world, with different legal systems. Most have some type of copyright law, and that law roughly follows international treaties. I have confidence that in the countries with "reasonable" copyright legislation/jurisprudence, that copyright licenses have force. Given that even the US situation is not entirely settled, I have no confidence that a public domain declaration has force in other countries. Therefore caution would indicate that a simple permissive license is preferable to a public domain declaration.
Therefore yes, I would say that the chances of Damiel Bernstein being wrong on this are good enough that a simple permissive license is preferable to a public domain declaration.
Public domain is explicitly part of the Berne Convention. Bernstein is, as CS professors go, atypically engaged with the law in general and copyright particularly. I wouldn't be too quick to dismiss him.
Berne Convention uses the term "public domain" as something that happens to works when copyright expires (absence of copyright), but it doesn't mean you can say an incantation like "i hereby release it to public domain" to make that happen. In many (most?) countries the incantation doesn't have a defined legal meaning as authors always have copyright to their works, the Berne Convention is implemented in national copyright law without talking about "public domain".
Bernstein may be right. He certainly does care about this issue, and has researched it. But when there are two almost equivalent approaches, one has 0 risk, and the other has minimal, why not follow the approach with 0 risk?
Incidentally your Berne Convention argument is rather weak according to my reading of the actual text of the Berne Convention. (See http://www.wipo.int/treaties/en/ip/berne/trtdocs_wo001.html for the text.) Public domain is only referred to in article 18, and the only type of public domain referred to is due to expiration of the term for copyright. Section 7 indicates the minimum terms in question, and those terms are both long and do not contain anything indicating that they can be shortened by the author's wish.
Therefore the fact that public domain is mentioned in the Berne Convention does nothing to reassure me that countries which sign the Berne Convention will necessarily pay any attention to a public domain declaration.
They recognize that the public domain might not exist in all legal domains, so a licensed version is available, for a fee.
Others have decided to decline to use copyright protection. There's a list of such software at http://unlicense.org/ .
I wouldn't look to the Berne treaty for some statement of the international existence of copyright law. You need to look towards national laws instead. For example, the US recognizes the public domain, and a work of the United States government is automatically in the public domain in the US. (Though it might not be in the public domain elsewhere.)
So like any social movement, if enough people release software and disclaim copyright protection, then those jurisdictions which don't recognize the public domain might change. If no software ever takes the risk, then it will never change.
> Public domain is explicitly part of the Berne Convention.
That doesn't mean the legal/IP system of Berne signatories has to allow putting things in the public domain before copyrights on it expire.
In fact, I know for certain that France does not allow it under any circumstance. And I believe (though without certainty) that this is the rule in all EU countries.
As Bernstein indicates, Lawrence Rosen argues the other side of this. There is binding precedent on the question in the 9th circuit. However that precedent is not necessarily binding on other courts, the statute does not provide for such a mechanism, and we've already seen statutes bring works back under copyright which had been out of copyright. The most famous example being It's a Wonderful Life. Therefore it is possible that other courts could decide differently, and it is possible that future copyright legislation or treaties could alter the legal status of works that have been abandoned to the public domain.
And this is just the situation in the USA. There are about 200 countries in the world, with different legal systems. Most have some type of copyright law, and that law roughly follows international treaties. I have confidence that in the countries with "reasonable" copyright legislation/jurisprudence, that copyright licenses have force. Given that even the US situation is not entirely settled, I have no confidence that a public domain declaration has force in other countries. Therefore caution would indicate that a simple permissive license is preferable to a public domain declaration.
Therefore yes, I would say that the chances of Damiel Bernstein being wrong on this are good enough that a simple permissive license is preferable to a public domain declaration.