@nixCraft f s
I am not suggesting this happens, but if someone was to submit a kernel patch that can detect say the domain the kernel is being run on then shuts down the kernel, it could very easily shut down facebook in an instant.
This would not be malicious, but an ethical thing to do given what they have said about Linux, so they can't be any ethical or moral reason for facebook to run Linux on their server.
Technical reason is that it is the best platform to run on, Facebook could easily switch to Unix and stop freeloading off the very community who they now consider 'bad' people.