Babies can suffocate from unsafe cribs as much as they can from unsafe co-sleeping.
I think the point is just to be safe with whatever sleeping choice you have.
For me personally, I will not let anyone except for me sleep next to the baby. Our first child will go into her own bed when the next baby arrives, and my husband definitely cannot sleep next to the baby, he is a very deep sleeper and rolls / throws elbows / etc. without realizing it (he's given me bruises in his sleep, haha). I keep the baby on the side against the wall, me in the middle, my husband on the "open" side. I don't take any sedative drugs or go to bed intoxicated in any way. I don't put blankets or comforters over a young baby, I just dress in a long-sleeved PJ shirt, and dress the baby warmly. I sleep with my head on the edge of a pillow, so that there are no pillows in the baby-sleeping area.
I'm sure you can research more guidelines for safe co-sleeping, but someone's baby smothering while co-sleeping is no more a reason to not co-sleep, than someone's baby smothering while in a crib would be a reason to not crib-sleep. No matter where the baby is sleeping, you just need to be careful and safe, no soft pillows or plush blankets that a face can sink into, no drugs or alcohol, only the mother sleeps next to the baby, etc.
ETA: "drugs" does not just mean illegal drugs, either. Any over-the-counter or prescription medication that says "may cause drowsiness" or "do not operate heavy machinery", not good for co-sleeping.
Kelly (28), in love with husband Jason (38) and our awesome babies: Emma 4/09, and Ozzy 8/10