Containers already fully depend on a shared and complicated kernel to do containment (which is why some say "containers don't contain" e.g. http://www.projectatomic.io/blog/2014/09/yet-another-reason-... ).

Virtual Machines have a smaller attack interface to the host, so they do have a chance of containing malicious code.

Kernels were supposed to contain processes, providing them with a virtual private memory space, virtual storage access so they can't read or write any file you don't want them to, etc... but only openbsd is really trying to make that work.