include fb.h from userland?

I understand that the headers in /usr/include/linux shouldn't be overwritten by new kernel installs. But can someone elaborate on Linus's original admonition (http://kernelnotes.org/lnxlists/linux-kernel/lk_0007_04/msg00881.html)? Am I never, ever, ever allowed to update my system headers for the

include fb.h from userland?

I understand that the headers in /usr/include/linux shouldn't be overwritten by new kernel installs. But can someone elaborate on Linus's original admonition (http://kernelnotes.org/lnxlists/linux-kernel/lk_0007_04/msg00881.html)? Am I never, ever, ever allowed to update my system headers for the