"There is no evidence that bed sharing is hazardous for infants of parents
who do not smoke."

This is the only conclusion one may draw from the available evidence.  That is why it is written that way.  The evidence does not show conclusively that co-sleeping is beneficial or protective, it only shows that bed sharing is not hazardous as long as the parents don't smoke.
Jalana asks whether this is just another way of discouraging co-sleeping.  For children of smokers, it is indeed meant to discourage co-sleeping, because co-sleeping poses an increased danger to those children.  Or you could view this statement as a way of discouraging smoking in parents with a strong desire to share their bed with their infants.  
There is evidence (from a joint Nordic SIDS study) that smokers who sleep with their infants dramatically increase the infant's risk of SIDS, even beyond the already increased risk from simply living in a smoking household.  The mechanism is not understood.  There is also evidence that infants of smoking mothers who do not breastfeed are at even higher risk of SIDS, so we should be encouraging smokers to breastfeed to offset the very serious negative effects their habit has on their children's prospects for survival.
Very little advice given by health professionals really has to do with life and death issues.  This is one exception.  We should be aware that tobacco is an extremely dangerous substance and that we have a responsibility to let parents have correct information about minimizing the risks to their children if they wish to continue using tobacco while parenting.  We should be letting this information reach parents even if some parents will feel guilty on hearing it.  What about how we would feel if a smoker's co-sleeping baby died of SIDS and we knowingly had not mentioned this information because we didn't want to make the parents feel bad, or not like us?  How will they feel about us when they find out we had so little respect for their decision-making skills that we didn't bother telling them how to reduce the risk?
As much as we intuitively feel that co-sleeping must be right, it does not allow us to make unsubstantiated claims on its behalf.  I think the BMJ conclusion is strong enough as it is.  I can argue with sceptical pediatricians on the basis of that sentence alone.
The recent debate in Norway is whether it wouldn't simply be safer to warn against co-sleeping for all parents, so as to spare the smokers hurt feelings, or whether we should simply make the facts known.  Guess which side I am on?
Rachel Myr

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