I don't do either, drinking or smoking that is. It's not because of religion or love for myself, it's just a personal choice I hold at the moment. With that said , I used to smoke and drink. My reasons for drinking and smoking don't matter because in the end all reasons are just excuses because you either want to or you don't.
I smoked for about two years before I came to the realization that smoking is utterly pointless and serves as no greater good or benefit to anything except the pockets of the government and the cigarette companies. Of course I knew and was told this before I started smoking but do teenagers really care? No, all they care about is fitting in and looking cool and whatever other reason they start smoking. Plus having asthma and being a athlete were also factors in my quitting. My smoking really alienated me from sports and my fellow athletes, they didn't understand how I could be so stupid.
My history with alcohol is a long drawn out and ultimately pointless story, the fact of the matter is I stopped drinking alcohol over a year ago and haven't touched a sip since. There is really no reason as to why I stopped I just did, I never sat myself down and said "Ok self no more alcohol." It just happened. Oddly enough it had nothing to do with the fact my friends often called me an alcoholic and the residence(university dorm) staff's suggestion that I join AA on campus. I guess I just grew tired of being drunk all the time.
So I maintain that smoking and drinking is pointless and there is no reason why someone HAS to or SHOULD. But if you decide to that is you're decision and as long as it doesn't hurt anyone except yourself go for it because everyone knows what they are getting into before hand.