Yep, old-school cigarettes are vile, disgusting things which lead you to a miserable lung-cancer death. Avoid ever starting since it is so hard to quit.
I guess it more depends on person, some try it and get addicted. I can talk from my perspective. I tried cigarettes few times when I was very young, but I didn't liked and didn't become addicted. I smoke on extremely rare occasions now, but actually forgot when did I bought cigarettes last time.
There’s no benefit of smoking. There’s nothing it does other than slowly kill you. If you want to lower stress and anxiety, there are so many ways to get that done. Some people even smoke electronic cigarettes thinking they are being smart but they don’t know that it’s just as dumb as smoking an actual cigarette. The carbon monoxide you say binds to hemoglobin in the blood, and reduces its ability to carry oxygen to his vital organs and tissues in his body. This can lead to a handful of problems that he probably doesn’t know. Encourage him to quit smoking. If he needs help, help him seek help. Or someday you may not have him any more.
I think that most people who smoke are aware about these things. I doubt that anyone thinks that's healthy to smoke, but they still do it. It's their choice, same like people choose to drink alcochol, junk food or too much energy drinks - none of these aren't beneficial for health too.
Anyway, no matter how you will live, what you will drink or eat, in the end most likely that you won't be healthy when you will die.