I mean strictly positive from a general welfare position. Competition through innovation is not a negative externality or else the automobile would be a negative externality on account of wiping out the horse-drawn carriage industry. And the camera and photography would be a negative externality because they eliminated most of the portrait drawing industry.
Automation will of course harm whichever sector of the economy remains on the manual processes, but it leads to more abundance overall.
Even the people who lose jobs due to automation are better off overall. If you personally consume goods and services produced by 100 different classes of professionals, and you yourself work in one of those 100 classes of professional work, and your job gets automated, you lose out in that narrow sense, but you gain from having the products and services produced by the other 99 classes of professionals, become more abundant through automation.
With respect to authenticity, that's easy to prove. Take coffee for example. People are willing to pay more for coffee that was made by hand. So what do companies do? They simply have the baristas make the coffee in front of the customers. Market incentives will produce efficient ways of proving authenticity.