Exactly the point, indicating that root can alter the SAK, which means it cannot be trusted.
More than anything else, this reveals why you are a suit and not a computer guy.
You live in a world of abstractions, coming from the top down, enforced by willpower,
rather than from the physical world, aware of what can actually be accomplished in hardware.

Do you think that, by putting security into a proprietary black box, totally inaccessible,
except, perhaps to the original designer, that we can all be happy and trust
a machine that refuses to trust us?

http://www.acm.org/classics/sep95/

http://catb.org/~esr/jargon/html/B/back-door.html