Stevan Harnad has always been insistent on the need for immediate, free access to academic research, and he sees self-archiving as the means to this end.
Now that he recognises that self-archiving may only be compatible with some publishers if there is a delay in access, Stevan (who is normally uncompromising, e.g. "OA itself is non-negotiable") seems to have accepted this fudge, which is not immediate free access: "Access to the immediate deposit can then either be set as Open Access immediately, or (in case of a publisher embargo), as Closed Access, provisionally". This is the "Immediate-Deposit & Optional-Access" (IDOS) policy. Even with a fancy name, and as Jan Velterop has noted, it's not open access.
Stevan has been adamantly against the crystal-ball-gazing that predicts a loss in subscriptions resulting from self-archiving, but his own crystal ball predicts that following a universal adoption of 'IDOS' repositories, "Embargoes will disappear very soon thereafter" [my emphasis].
Stevan has criticised advocates of open access journals who claim that open access journals will reduce costs, as he insists that it is access that is paramount and not costs, which is a fair point. Yet he now criticises open access journals and hybrid journals for the extra costs he says they impose, for example criticising CERN's decision to put up funds to pay for article processing charges as "diverting scarce research funds from research to paying publishers". It seems that if open access journals might save costs, that's a side issue; if they might cost more, we should take heed.
While there might be issues with double-payment in hybrid journals, that can be corrected by adjusting subscription costs - it isn't an insurmountable issue. Further, open access journals don't have this problem, but Stevan's criticisms of Springer Open Choice don't often allow for this distinction. How open access can be paid for is open to debate - the debate has usually focussed on the article processing charge, but as Peter Suber has noted not all open access journals charge author fees. Costs can also be met using advertising (though hardly an uncontroversial way for a medical journal to recover costs), grants from societies (this is how the Beilstein Journal of Organic Chemistry is funded), charitable and philanthropic donations, or even by cutting costs. An interesting aspect of article processing charges is that they can result in price competition on an article-by-article basis.
Rather than being a system with no barriers to access (the definition of open access as I understand it), under self-archiving each author (having signed over copyright to the publisher) needs to deposit their articles in their local repository (if one exists), then each reader needs to realise that the repository exists, find the article, and then possibly have to contact the author to get a copy, and then have the author respond and send it to them. Sadly, this seems to be laborious, incomplete and prone to failure. I had thought that the launch of Google Scholar opened up the possibility of self-archiving really being viable, but their practice of linking to all copies of an article that could be found on the web only lasted a few short months and links to free versions are now intermittent - possibly (probably), Google were sat on by publishers.
Libraries will apparently continue to subscribe to journals that their users can access at no cost, despite evidence that libraries are acutely attuned to cost, and an existing trend of university actions against high journal prices. Publishers will apparently be happy to have a business model that depends on their customers paying for a product that can be obtained for free. This business model is actually seen in shareware, though shareware is much rarer now than 10 to 20 years ago, and certainly the music industry isn't too keen on this business model. If self-archiving doesn't cause a collapse in subscriptions to closed access journals, I'd suggest that it will implicitly have failed to achieve its goal. Surely the aim is to provide immediate free access to peer reviewed academic research - if libraries and readers are unaware that they could get what they are still paying for at no cost, might that not imply that self-archiving doesn't provide universal access? Might there be those who aren't paying and who don't realise that the research is accessible, and therefore never read the article? We need to end this farcical situation of researchers not reading articles, and although I like the idea of self-archiving I don't believe that if offers a complete enough solution, or is sustainable.
Stevan's insistence on self-archiving has even extended to criticising central deposit in PubMed Central, arguing that articles must only be deposited in institutional repositories. What is BioMed Central to do; stop depositing in PubMed Central? It's hardly as though we block our authors depositing in their own local repositories.
Stevan lays claim to being the true voice of open access. In responding to an article by Ben Goldacre he argued that "It is not "two [Gold] OA publishing organisations" that have led the fight for OA, but one (Green and Gold) organisation -- the same one that first coined the term OA in 2002: the Budapest Open Access Initiative (BOAI)". Actually, it's not true that BOAI coined 'open access'.
Stevan at times appears to be entirely opposed to the idea of open access journals (despite apparently supporting the idea a decade ago), for example raising criticisms against BioMed Central as a publisher from the outset.
I can't agree with Stevan's insistence upon local institutional self-archiving to the apparent exclusion of other approaches to open access. It appears to me that with archivangelism the means has become the end.