Because they won't fight back...

[Happy Monkey]

Originally Posted by 9th Engineer

The only material we need to work on is how long we can braid carbon nanotube strands,

I hope so, but manufacturing will have to become extremely exact, as the tiniest flaw dramatically decreases the strength of a nanotube. And I don't know the physics, but I can certainly see hard radiation, drastic temperature differentials, and space-dust impacts could cause imperfections even if our production methods are perfect. Some form of continually-replaced shielding would probably be needed, which would dramatically increase the weight of the cable.