Heather, thanks for your comment. While I agree that in most situations, nothing bad happens secondary to co-sleeping, the potential is there for a mother (or a father) to fail to recognize their impairment, even if they think they are a light sleeper. We have plenty of evidence that people fail to recognize that they are "under the influence" when they go to drive a car, and can end up having a crash. Some new parents can be so tired from chronic lack of sleep, that even someone who is traditionally a "light" sleeper, such as myself, can occasionally sleep so soundly, they don't wake up with minor noises or when they roll over on the infant.
I kept my newborns in a box-like carrier with handles, that I was able to put in the bed or next to the bed as necessary. It kept them safe, was hard and sturdy, and prevented either of us from rolling over on the baby. Yet they were right there when they needed to nurse. Obviously we occasionally will fall asleep with the baby when they nurse in the middle of the night. But when I realized it, I would return my little one to the safety of her "box" and I know I was then able to sleep more soundly thereafter.