Why would an intelligent adult eat unhealthy and become obese or drink alcohol that causes a variety of health problems or do any number of unhealthy or unsafe things? We do these things because we enjoy them or because they help fill a void in our lives or they make us (briefly) feel better or because its become a habit that ingrained into our routine or any number of other (usually bad) reasons. It's just what people do. Most people have some vice or another. We're only human.

I think everyone starts smoking because they think it's cool.

Couldn't tellya. I wouldn't touch the stuff with a barge pole and the fastest way to get me to leave is to light up any of that shit.

Never have used it, never will. Too many family members died of smoking related cancers for me to be curious enough to try it.