Is co-sleeping irresponsible?

Last weekend, while driving home from the airport, my mom saw a huge billboard near a major hospital with a picture of a pretty female doctor that read:

“I’ll be the last one to see your baby. I do autopsies. Never sleep with your baby.”

Is there really strong enough medical evidence now that cosleeping endangers infants? I thought the debate was mostly philosophical and a matter of personal preference. Such a strong statement is tantamount to something like “on demand nursing of infants causes childhood obesity”.

I don’t practice cosleeping because (1) I sleep poorly with a fitful newborn beside me, (2) it unnecessarily trains the baby to rely on my presence for sleep, (3) the baby sleeps less soundly and (4) realistically if the baby is in our bed my husband is often sleeping somewhere else, which upsets the marriage-comes-first order of our family. Besides, the attachment parenting “womb theory” (attempting to continue life in the womb for an infant by cosleeping, on demand nursing, baby-wearing) overlooks the obvious reality that the child is no longer in the womb because he has developed beyond the need for a womb environment.

However, with my last two babies, in the first three weeks after birth, I have coslept because it seems to facilitate just slightly more sleep for everyone in those first hazy weeks. If cosleeping is truly unsafe, I’d like to know more about it. Queen B and other medical experts, could you provide any commentary?