I think he's far more worried about the bullets whizzing by him than he is about how his lungs will look in a few decades!
Exactly. Those Marines in Fallujah are living minute-by-minute, second-by-second. They're not thinking of the long-term consequences of anything right now. And if a few smokes helps them calm down and get through the day, then I'll be the last one to say anything about it. They can worry about quitting later.