Well, it does seem unreasonable to call Hensher ungrateful; like anyone Hensher has no duty to write except when it pleases him.
But Hensher does talk about how this would affect those with aspirations to be writers and I don't think we should do anything to encourage young people to become professional writers. Yes, let's encourage them to write, but don't sell them on the dream of making their living that way, because for all but a few people, that's just not possible.
Simply, there are lots of people that want to write, but the number of people paying for writing isn't enough to support very many professional writers. No different than anything else. I may be a Tai Chi master and want to teach Tai Chi (I don't even do Tai Chi, this is just an example), but Tai Chi is something people enjoy doing and there are many other instructor level Tai Chi practitioners. But that doesn't mean there are enough paying Tai Chi students to support all of us.
There was no link to the actual words each wrote in their conversation, so the whole brouhaha might be artificially amplified (eg. One party might have been rude or arrogant, the other might have just reacted).
Besides, there is a confusion in one of the arguments between getting content for free and getting authors to work for free.
The profound sense of entitlement of professors like Webber can fairly be called disgusting. Some--make that many--successful academics have no compunction whatsoever about exploiting the time, energy and experience of others.
I recently left academia on account on account of the exploitative culture and then declared an eternal moratorium on low-academic-value, unpublishable or otherwise uncredited technical work for academia. Perhaps I should start a movement called Technologists Leaving Academia.
From the situations I've been aware of, I believe this is certainly true in the world of programming books. However, typically someone will write a foreword and have quite a bit of latitude as to what they do, so it's more an honor than anything.
With more academic books, I've noticed that the forewords are more substantial and will refer to the contents of the books and other research in a more precise way. As such, I suspect they're a lot more work, whereas you could bash out a good 3-4 page foreword for a programming book in a few hours if you had the relationships or experiences to lean on.
But Hensher does talk about how this would affect those with aspirations to be writers and I don't think we should do anything to encourage young people to become professional writers. Yes, let's encourage them to write, but don't sell them on the dream of making their living that way, because for all but a few people, that's just not possible.
Simply, there are lots of people that want to write, but the number of people paying for writing isn't enough to support very many professional writers. No different than anything else. I may be a Tai Chi master and want to teach Tai Chi (I don't even do Tai Chi, this is just an example), but Tai Chi is something people enjoy doing and there are many other instructor level Tai Chi practitioners. But that doesn't mean there are enough paying Tai Chi students to support all of us.