Well you could have managed images in a VM, many do that, incl. ppl just using ec2. you could also do that using lxc, or what not, not necessarily with docker.

So basically, ocker adds nothing to these other solutions except complication, bugs, etc. (which is also my experience).

Moreover, and to push it a little further, if anything, it's a better idea to call some container library so that you use namespace for your very use case, inside a VM. That VM being an image that you manage and deploy of course (ie that you dont tweak when its running unless its for debugging)