Earlier quoted context omitted.
Look at it as at a bad but addictive habit. Hundreds of millions of smokers do harm their health, and through it their own and their neighbors' wealth. But quitting is indeed hard.
You can’t seriously compare smoking and keeping up with friends and family, which is the reason that drives most of the usage of Facebook.
You're right: It's easy to smoke outside without harming anyone but yourself -- and even if you smoke indoors, you only harm one room full of people at a time.