The claim that horizontal scaling is free with Docker is simply not accurate.

Maybe it will be some day, but these orchestration and deployment tools built on Docker have enormous hidden costs.

IME, Docker takes an enormous amount of focus away from the customer problem and moves it to the how to get this mess working problem.

Now may be the right time in a given business to make that shift in focus, but to claim that it will be "free" is just misleading (IME).