I'm sure people are going to fall into two camps with Google's Duplex: you're for it, or you're against it. Ethan Marcotte has a nice write-up about the latter, specifically with regards to how Duplex was designed to deceive.
...the demos above are impressive because Duplex specifically withholds the fact that it’s not human. The net effect is, for better and for worse, a form of deception. Duplex was elegantly, intentionally designed to deceive.