Does Linux support multi-user?

True, I forgot completely about that one. We have actually used it here in one project, but to isolate only one "untrusted guest" from the host system. Haven't thought about running tens of containers, but I could imagine that the overhead is pretty low especially compared to VMs.

But lxc would not help to get more consensus about these security "issues" this discussion started from. If the kernel were affected by some information disclosure or denial of service issues, in many cases the issue would not be limited to processes running inside the same container.

So the nice argument that within one container we can just talk about a single user system and don't worry that much about about information disclosure/denial of service/pro-active security would just not apply to many cases. No free lunch this time either :(