I don't work for Alaska, so take everything I say for entertainment purposes only on this subject.
Nicotine is not the enemy. The use of tobacco products is. There are multiple illnesses associated with tobacco use. My Mom smoked for 49 years and died as a result of conjestive heart disease and emphasemia. She did not have a cancer. Lost work due to tobacco use illnesses may be one factor in Alaskas decision. I may suggest that you contact the Human Rescources department at Alaska on why that is a requirement to work there and report that back here on this thread.
I agree that alcohol and nicotine are not illegal substances, but as a flight crew member, you may not use alcohol when you wish, as you wish. In many municipalities, it is illegal to smoke in many establishments, ie, bars, taverns, restaurants, etc. I saw in todays newspaper, that you may not smoke in any Westin Hotel property after January, 2006. If you do, there will be a $200 surcharge added to your bill.
The bottom line is that your employer may restrict the use of some consumer products, if that is a condition of your employment there.