Hard links to directories: why not?

[William Lewis]

   In the man entry for ln(1) (and for link(2)),  it says that
hard links may not be made to directories, unless the linker is
the super-user (in order to make '.' and '..', I suppose). My 
question is: why not? (and is there any reason that I, if I'm
root, shouldn't do this?) It seems perfectly harmless to me, although 
it would allow the user to make a pretty convoluted directory structure,
that's the user's priviledge. So I suppose it's probably a security
issue somehow (restrictions of this sort seem to be). Hence the
crosspost to alt.security. 
-- 
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