I am an author with three books on there, and I've just emailed them to opt out. One reason authors are fine with libraries lending out their books for free, electronically or otherwise, is that borrowing a library copy is always a little bit less convenient than buying your own – with waits for availability and so on – which gives readers an incentive to pay if they can afford it. Once the library experience is almost indistinguishable from the paid experience, there is no reason for anyone to pay except as a kind of donation to the author. Yes, some generous people will choose to do this, but others won't, and we lose sales.
I am a mid-list author. I am not so successful that I will do fine whatever happens, nor am I so unsuccessful that writing is just a weekend hobby for me. Like many authors, writing is my career, but it's on a knife edge, and every sale counts. I've sat for an hour at a signing table just to sell four books, and I would again.
I spent five years working on my last book. People complain about 'legacy publishers', but I couldn't have done that without the support of a legacy publisher. Everything that further chips away at my sales reduces the chances that my publisher will be able to support me in the future, and so it reduces the chances that I will be able to put that same time and effort into another book. By 'liberating' the literature of today, these people are strangling the literature of the future.