For me, it's the simplicity. I don't have to care whether a project is super basic, or a thorny hairball from hell. Whatever it is, "docker run" is how I spin it up. It doesn't infect my local. I can have three differently hobbled versions of it side by side. Virtualization makes it simple, conceptually - and for me that's more precious than it being actually technically simple.
> I don't have to care whether a project is super basic, or a thorny hairball from hell.
That's the biggest problem I see with Docker: nobody has an incentive to make well structured software with a lean dependency chain and a straightforward installation process… These used to be good proxy of the overall software quality of the project, but now Rube Goldberg projects that just happen to work by luck are routinely distributed and the user has no idea of how big of a mess it is internally.
