The primary rationale behind these policies has been frugality, citing greater insurance-costs for smokers, and the savings implied by eliminating them from the workforce. In some less aggressive situations, persistent smokers are imposed a "Tobacco User Surcharge" of $20 per paycheck and offered waived co-payments for smoking-cessation drugs.
Efforts to cut expenses and encourage better health seem perfectly normal. Policy prohibiting activities otherwise legal, but unbefitting a workplace environment also seem normal. However, employers or government defining employee's domestic lifestyles is a relatively new concept, especially when nothing illegal is involved. It would be difficult, if not impossible to argue that smoking is without consequences; but is breeching the boundaries of the household inconsequential?
Times do change, and adaptation is often a necessary burden. But have they changed so much that we'd now postpone the Manhattan project for 12 months because Oppenheimer had toked his pipe? Would we confine our vision to the Milky Way or snub the 1373 Cincinnati because Hubble smoked his? Would we shun relativity, or shelve the works of Tolkien because he and C. S. Lewis had done the same? If so, then where will it stop? Will we soon scan employees for signs of excessive sugar, trans-fats and cholesterol? Will we have authenticated and logged aerobics classes? I, for one, welcome answers from our new salubrious overlords.