Stevan Harnad is a forceful advocate for open access, and I agree with most of what he advocates. I do have a different view than he does about the connection between open access and copyright and his analysis of the Harvard policy calls this to the fore.
My response is essentially the same as Peter Suber's. I'll add that Stevan characterizes the policy as reservation of rights. I think that's mistaken. Under the policy, the author continues to own all of the exclusive rights under copyright and remains free to transfer all of them to a journal publisher.
What the Harvard policy calls for is a non-exclusive license, which is the same thing as permission. All that the FAS have done is agreed that they have granted Harvard permission to post their work in the repository and that Harvard may grant others similar permission so long as copies are not being sold for a profit.