Substance abuse is incompatible with safety in aviation.
I'm not convinced that the term 'substance abuse' should be applied to nicotine. You could argue it both ways but there is a huge stigma associated with 'substance abuse' so probably best not to use the term.
Many, many firms - not just in aviation - refuse to employ smokers. Period. I don't know what the legal situation is in the UK/EU or elsewhere but surely all of us here must know that to be true? I gave up when it got to the point that I was always craving a ciggie -- shops, restaurants, certain workplaces (this was before the blanket EU ban in buildings) etc. I reasoned that I might as well get the grief over with and have done with it.....it worked but it was hell, to be honest.
I see friends with electronic fags today, with little lights on the end and 'smoke' emanating from them. I think they have just transferred their addiction to those, because they are so realistic. Presumably they are safer health-wise, they are not hot so cannot cause damage and seem not to smell as far as I can tell so won't offend even the fussiest other than those who object to their pilots having nicotine in their blood per se, a group I don't have any time for, honestly. Apparently not everyone allows these to be used in non-smoking places? If they are allowed, maybe it's the answer for flight-crew?