Sam2 she said it was pikuach nefesh. He was responding to that. He didn’t say it was mutar.
LU many young guys start to smoke for various reasons, foremost and stupidest among them is to feel cool. Many of them keep smoking all their life. The way to fight that is to be critical of smoking. By saying it’s understandable and that a girl who wouldn’t go out with a smoker is illogical you are encouraging it.
A girl might still choose to go out with a smoker if she understands that people aren’t perfect, and that she isn’t perfect either. Smoking is very bad and smokers are human. Why can’t it be just that?