It's not even necessarily a matter of inattention. Imagine that the autopilot was driving along just fine, and when it was just a few feet away from the parked cruiser suddenly veered towards it for whatever reason. It might be physically impossible for any human, no matter how well they are paying attention, to intervene and avoid a collision.

I'm not saying that's what happened, but it's certainly possible. The mere fact that it's possible to me casts doubt on this entire design philosophy.