That does sort of imply that some damage is being done, yes?"
Yes, it does. And I also don't think it is a good idea, but should it be illegal?
Our grandparents painted their houses with lead paint, used asbestos gloves for removing hot items from the stove, etc... and somehow they still lived for a long time, e.g. my Mom is 89 and is still going strong.
Equivocation Fallacy! You are attempting to establish a false equivalency, by comparing an adult, in the 21st century, lighting up a cigarette (a known and recognized hazard) in a motor vehicle with a strapped-in infant, and some old folks in the previous century voluntarily engaging in activities which, at the time, were not known to be associated with cancer risk.
You know that you are making an invalid comparison!
Regards,