If you want to use Docker then you can go ahead - I don't see anyone claiming that this brand new, highly experimental project should be used by everyone instead of Docker.
There are tradeoffs hers. For some people the tradeoff of a single executable file with everything in it compared to setting up a Docker system is worthwhile.
Do you routinely download unsigned binaries of unprovable provenance and run them? Because if you do, you might eventually find reason to appreciate the additional isolation that namespaces et al give you very conveniently via Docker (or your favorite alternative).
There are tradeoffs hers. For some people the tradeoff of a single executable file with everything in it compared to setting up a Docker system is worthwhile.