Re: Yep. Docker Con.
There's no con here unless you take the view that the kind of functionality provided by Docker and containers should have been subsumed into the operating system years ago.
While Linux is volunteer led and so lacks the resources to lead on such a scale, there's no reason why IBM or Microsoft couldn't have innovated this for themselves 10 years ago.
In a similar vein, and while I'm on a mini-rant, it's a similar situation to Java. Why do we still have Firefly/JBoss, Websphere and Webserver when it could all be subsumed into the operating system?