On the other hand it's no insanity to run millions of lines of code in a computer, connected to the internet and hopefully sharing all the projects you need to

On the other hand it's no insanity to run millions of lines of code in a computer, connected to the internet and hopefully sharing all the projects you need to work with and dependencies you need to make them work, with full access to your filesystem, usually requiring administrator rights to be installed or even used. This would all be needless if there was an OS that allowed you to switch to another "env" wiping the RAM in the process (like, storing a snapshot of it for when you switch back), with guaranteed isolation at the filesystem level (perhaps able to still read-only link into common libs), able to install things without touching other "envs". If you're working in any webdev related environment, that is itself the definition of insanity. It's like buying a hammer from the carpenter at the end of the road and giving access to all your house to him in the process, including your wife. Everything becomes a nail.