Firstly, I think it is correct that docker encourages disposable infrastructure, because your docker setup basically must be able to recover from the loss of a container. I think it would not be sane to expect your containers to "just keep working".
Regarding security, I don't think Docker provides much other than the illusion of better security at the moment. At least on Linux containers don't add security that you can't get with traditional services.
I suppose if you use authenticated images you can at least be sure that you're running the code you think you are, but then again package managers have had signing for ages.
You're always going to have to test your software in the environment you will be deploying it in, because driver bugs and weird interactions still exist. Docker doesn't really let you ignore the hardware
I have no opinion of kubernetes and such at the moment.
What docker does grant is an easy method of "packaging" software... Pretty much anyone can just throw everything together in a big bundle and distribute that. For certain use-cases, this can give a development team much more speed, since setting up a workable environment is much faster. There is also a nontrivial amount of software that simply does not bother with OS packaging where containers can help you deploy it in a more controlled fashion.
