I think what he's saying is that co-sleeping provides benefits to his family. While there are risks, it's difficult to discern what the increased risk is in the absence of drugs and alcohol. He feels that there may not be a causal link between SIDS and co-sleeping for families who take co-sleeping seriously and take steps to minimize the known factors in SIDS.

It's not a great argument necessarily, but people accept additional risk of injury to their kids all the time if the benefits outweigh the risks.