It's not why would anyone question the intelligence of smokers, but why would anyone not?
Yep. With all the medical evidence that proves to us that smoking is a health hazard, you still see people taking it up, and some smokers claiming they know better than the medical experts who have spent years researching the issue.
I know one woman who is always ill, forever taking time off work, and claims her doctor has told her that she shouldn't give up the gaspers because it would create more problems. She just hears what she wants to hear. Now if that's not a case of mental deficiency, what is?