My understanding is that they are implying interstellar travel, because of its complexity, would be impossible without some form of consciousness in charge to steer things.

I'd argue that evolution has accomplished plenty of incredibly complex designs without an ounce of consciousness in play—much more complex than anything humanity has made. And I'd add that even we puny humans have been able to create intelligence without consciousness, meaning the concept of one being orthogonal to the other does not at all seem far fetched to me.

I think Blindsight quickly runs into questions which people will disagree on rather strongly, based on their beliefs and world views. Which I'd say is a marker of a good sci-fi book.