Smoking may be self medicating for depression and at least one study suggests smoking lowers the risk of death for people who suffer depression.

https://news.ycombinator.com/item?id=37923037

Some drugs that treat depression have a side effect of causing a lot of people to stop smoking. Maybe someday we will understand depression well enough to effectively and reliably treat it. At least until then, blanket statements about smoking aren't really reasonable.

I hate smoking. I have respiratory problems. I don't want people smoking around me.

But nicotine is a morally neutral chemical that, like any chemical, can have constructive uses.