But we aren't seeing common sense are we? Even here we have seen arguments that pretty much amount to that one must either wear a bourka or go naked in public.
I don't think for a moment that publishing a book especially about a fantasy world voids your right to personal privacy. If Tolkien had got famous by being a papparazzo or founding Wikileaks you might have a point on grounds of hypocrisy but Tolkien never tried to be famous. He did what he did for it's own sake. He surely would never have embraced the modern cult of vacuous celebrity or endorsed the making public of every last thought that passes through ones head or photograph of every moment of ones life. Can you imagine Tolkien tweeting? That many people have no regard to their own privacy (I am tempted to say have no shame) shouldn't deprive others of theirs.
I think someone of Tolkien's generation would have expected a private letter to a family member to stay private. Letters are more rare and significant now perhaps but back then it was the only practical method of communication - even when I was a child and teenager, not so very long ago (though shatteringly just before Lady Brooke was born - congratulations btw), I was expected to ask before using the phone because of the cost. Would you find it intrusive if you had your private phone calls recorded and published? I know I would.
Yes it is sad for the authors if they have wasted work but they were exploiting resources they had no right to. The copyright laws regarding letters is hardly obscure. Given the history I am not suprised that the Estate protects its rights and privacy by what ever means available. If the laws it uses weren't designed for that purpose so what? You use the tools available. The professional body I used to belong to had a member who brought it into disrepute by major fraud and embezzlement. They could have used the associations rules on such things to expell him but it would have taken a long time and been expensive. Much simpler to expel him on grounds of non-payment of subscription.
The Tolkien family are not monsters. I am sure a lot of fans resent the estate protecting its rights re the Hobbit because it delayed the films. A lot of charities will be very grateful they did. Intellectual property isn't trivial because it is intangible. It protects the livelihoods of artists and writers. So the recipient has no right to profit from a letter. If I (as I sometimes do) send a card made from one of my original photographs) I woudn't expect to expect that recipient to reproduce that card and sell it for their benefit without so much as a by your leave.