[nl]

So, in the absence of strong AI, it's vastly more efficient to actually have a few humans on board the ships.

Have you done the math on that? Humans (and more importantly their life-support systems) are hugely, hugely expensive in terms of the carrying capacity of a space ship.

[vidarh]

There's also the rather large cost in reduced maneuverability when you want your on board humans to be able to survive.