It may be the case that PaXTeam's native language is not English. It would be obvious to all native English speakers that 'be able to trust that the content can't cause the filter programs to do evil things' is not the same thing as 'be able to trust that the content can't cause the filter programs to do any evil things whatsoever, forever, regardless of kernel bugs, cosmic rays, and Doctor Impossible', but perhaps it isn't obvious to a non-native speaker.
(More precisely, SELinux is sandboxing the *applications* so that bugs in the *applications* do not cause privilege escalation. It can't sandbox the kernel itself, and never has been able to: the most it can do is 'accidentally' prevent the occasional escalation if, say, some escalation depends on doing something to some entity that SELinux is in any case denying access to. I don't see how anything short of VMs could sandbox the kernel itself, and even then you're vulnerable to kernel bugs in the VM, as PaXTeam et al have said ad nauseam.)
(Perhaps Dan *could* have said as much, but I agree, it is ridiculous to expect every single blog post to come with a long disclaimer lest anonymous trolls rip it to shreds after misreading it. Every security solution has a vast list of conditions it doesn't handle: the place to document that is in the docs for the security solution itself, not in every blog post that ever mentions said security solution.)
(I fully expect to get a bunch of virulently offensive followups to this from the pax and grsecurity trolls, as usual. I don't care, they're irredeemable. It's other people who matter.)