Given that, it's not surprising their first reaction is anger. Perhaps not rational, but humans are not inherently rational beings.
The authors thought "Lend my book to a friend? Sure, why not? Good word of mouth always helps!" A nice, forward thinking perspective.
But what LendInk makes possible is for lending to extend beyond normal social connections. You could go look for any book you wanted, never buy another book again. And each book would be lent the maximum number of times. There's a fundamental difference at work there, the dynamic changes considerably.
You could say "Well libraries work the same way! Buy once, lend forever!" But libraries are geographically constrained. And there are a lot of them. So being able to be lent anywhere in the country still means you sold a lot of books. It's fundamentally different.
So while this site certainly didn't promote piracy and authors were compensated when appropriate, it did subvert the terms they had agreed to, and it did so willfully.
I can see where the content creators are coming from there.
This is probably a good idea, and probably inevitable and unstoppable. But that doesn't mean it has to be on the same economic terms as the previous model.