I have a friend whose husband was an older single boy until he married her. He smoked until he got married (she didn’t find out until right before they got engaged or she probably would never have ended up going out with him or marrying him). When he mentioned that he used to smoke, I was shocked because he is a really serious Ben Torah and very straight and shtark. He explained that as an older single boy (maybe even just as a bochur even w/o the older part), he needed an outlet. He needed to do something that felt “rebellious” but was not actually assur (at least not in the way that movies, hanging out with girls, etc. are), so that’s why he smoked. My impression is that is why a lot of bochurim smoke.
Until I heard that, I was very judgmental of people who smoke. But once he said that I could hear the logic in it. Personally, I still would probably be very reluctant to go out with someone who smokes, but I think that is an emotional reaction. The fact is that I would understand (to some degree) if an older single boy felt a need to watch movies occasionally, and smoking is certainly no worse (probably better).
It is also important to keep in mind that even if smoking is assur, I think that only applies to smoking an amount that would lead to addiction. I know a Talmid Chacham who smokes once a week because he said that doesn’t lead to addiction.
It is also important to remember that “hevei dan es kol haadam l’kaf zchus” applies to those who smoke as well. Tisha B’Av just ended and it’s almost Yom Kippur. Let’s try to judge favorably – maybe those people who are smoking would be doing something worse if not smoking.