Everyone was supportive of it when it was used towards the non profit digitization of out of copyright books. So, started externally, Google ran with it and continued and expanded the range of books. It remained good. Apparently loads of books were digitized.
Then, possibly along with the change in this article - or along with the perceptible change within Google where everything had to be business accountable a few years back, reCAPTCHA started being used to digitize address numbers from StreetView to improve Googles online mapping, geocoding offering. Nothing to do with books, nothing to do with improving the world.
Now reCAPTCHA is being used for image recognition and training (identify the images with salads). Nothing to do with books, information or improving the world - everything to do with Googles own offerings.
What's even sadder is that http://captcha.net/ still states that it is being used to "help digitize books" but all the links go to https://www.google.com/recaptcha/intro/index.html which have all but removed any public benefit wording. " "Stop spam, read books." was removed from Googles site in 2014.