Russell Blake, like a lot of authors, is decidedly pessimistic about subscription services like Kindle Unlimited:
"Subscription services will make it much harder to sell books. The voracious readers who are most likely to try an indie with a “WTF purchase” will instead tend to borrow instead of buy. This will result in drastic reductions in author take-home pay, all assurances of “increased exposure” aside. A whole group of readers are being conditioned to believe that books have little or no value/should be free/should only be read if virtually free. This will continue. For an idea of where this progression ends, look at music. Musicians can’t earn decent money anymore by having a hit, or even several hits. The economic model is broken in such a way that the artist sees virtually nothing, with the intermediary company that enables the download taking the lion’s share of the revenue. Musicians now earn their livings by touring, by selling merchandise (shirts, hats, etc.), by selling virtually anything but music. Alas, authors don’t have the option of filling coliseums at $50 a ticket or being cool or mainstream enough to hawk $22 concert T-shirts with their likenesses on them, so expect things to get much harder."
Blake is right—if (and only if) all books are forced into the subscription model stream.
But this is unlikely to happen, because writers will simply begin to withhold their work from such services. (As I noted earlier, musicians are already pushing back against the subscription model.) Writers are well connected with each other online, and it wouldn't take long for such a revolt to ensue should Amazon (or anyone else) attempt to mandate an exclusively subscription-based model.
And let’s not forget about the corporate publishers: They are unlikely to agree to a business model that basically gives away all of their product.
That said, even well known writers can benefit by making their work free (or practically free) in specific, limited circumstances.
The important factor here is strategy; and there are models to be found in other industries.
Nearly every consumer goods manufacturer gives away samples. (Haven’t you ever received a free sample of toothpaste or detergent in the mail?) These companies all experiment with loss leaders and the like.
The key distinction is that Procter & Gamble or Pepsi would never give away everything for free. Beyond a certain point, you have to pay them.
And herein lies the difference between a writer who strategically uses “free” as part of an overall marketing plan, and an insecure, approval-seeking writer who is eager for any scrap of validation.