Human beings are constantly doing things that would make themselves less combat ready, have a soda, stay up late, don't stretch, even getting your way once in awhile makes you less combat effective. The military is likewise doing things to military personnel that make them less combat ready. Exposing them to harmful fumes comes to mind. Before you argue how important whatever task they're undertaking is worth exposing them to these fumes, it's just as often busywork. Other military people will back me up on this.
Nonetheless most military personnel are indeed combat ready and are tested for their readiness, smoking is very popular in the military and it might shock you to learn that they just train hard enough that they stay in shape anyhow. Efforts to ban smoking on ships and things have caused MASSIVE problems, imagine that your entire day is shit and there are only four things you have to look forward to in a day, food, sleep, jacking off, and smoking. Your free time consists of 5 minute increments where you happen to be idle. These are the best parts of your day for sometimes months at a time and sometimes you're not getting sleep either. Then someone tells you that you can't smoke. People start falling asleep on station, even months later people are still irritable because they're not able to provide an artificial source of satisfaction in an otherwise totally unsatisfying way of life.
Forget that. You can't even imagine the sort of lives military people live. It's the SMALLEST of things that you get to enjoy and it's almost intolerable when you've already been injured several times or completed some sort of dangerous task and some safety nerd comes around taking your last bit of fun away. Imagine the stitches are still bleeding somewhere on your filthy body and someone with soft hands in a clean dry uniform yanks a cigarette out of your mouth and reminds you how bad it is for you, or when nobody has given a shit about you in a year and then someone has the nerve to tell you that people have heard you're drinking every night they're going to send you to drug counseling. When your day consists of working so hard that you think maybe you might pass out, but you keep working because you figure you'll pass out and get a few days rest in medical or maybe you won't pass out but man you feel funny and right while this is going through your head some guy tells you that they don't like you walking around without a shirt over your t-shirt. You're that guy.