As I said, there is evidence to correlate smoking with asthma (although that doesn't account for the ever increasing rates of asthma) but that doesn't show it as a direct cause and effect relationship. You can't just say smokers children have a higher incidence of asthma therefore smoking is what causes it, there may be other effects (e.g. genetics/social and environmental background etc) which haven't been investigated properly yet. But, to answer your more emotive point: No, I wouldn't be happy to keep a baby in a smoke filled room because statistically speaking it MAY harm the baby and I don't see smoking as something that can't wait until the baby isn't in the room anymore.