"effectiveness of VMs" is probably not what really mattered, but rather "disposable environments". A VM can be a type of re-creatable and disposable environmen

"effectiveness of VMs" is probably not what really mattered, but rather "disposable environments". A VM can be a type of re-creatable and disposable environment, if you also include an OS and configuration. But if all you need is a CLI context, the same could be said for chroot, LXC, Docker etc. A VM can be an easier mental model or box for people, but no all people are the same.