How are namespaces similar to microkernels? I see them a lot more as glorified chroot; it's not like there's a modprobe namespace or anything.
Then there is the whole IPC taking place across containers with much slower APIs and heavier context switch states.
The two remaining ones are worse than any micro-kernel API call in performace.
[1]: https://docs.docker.com/engine/reference/run/#ipc-settings--...