I'm not sure I quite agree with that. Having a controlled environment in a sandbox of its own clearly has benefits, both for consistency of what you're running

I'm not sure I quite agree with that. Having a controlled environment in a sandbox of its own clearly has benefits, both for consistency of what you're running and for safety if it doesn't work as you expected. It doesn't need to be Docker specifically that we use to create such an environment, but if not Docker then we'd surely have looked for some other way to achieve the same result.