In my industry, I would NEVER DISCRIMINATE against a smoker... I tell you why... 3 of the most competent colleagues that I know are smokers... They will wander off down stairs for a ciggie, clear the mind, have a little break... Gives them a moment to refocus, and focus on the more important things... The cost significant issues... Come back up, and plough right back into it...
There's another bunch of other people that have a break and start talking to each other, and now you have 2 or 3 people not working... (on company time

).
If I was employing, I would have these 3 "smokers" on top of my list!! Great blokes...
PS - I'm not a smoker.
PSS - I understand the concept... smoker is smoking, not working... When your work requires thought, or deep thought, a smoker can kick back and "think" about the important things... Smoking breaks can actually be quite productive for some people, in certain professions... Engineering, Design, Creative Arts... Flip side, a smoker in a call centre needs to stop their mundane work for a ciggie... Two sides to this coin peoples!!