"Then again, I also think people who have diseases from drug abuse such as kidney/liver failure from drinking, lung cancer from smoking, hep-_ from shooting up, etc should be completely denied medical care. You made your bed, now die in it."
Interesting that you didn't include obesity and lack of exercise. That is arguably causing a lot more illness and costs to the healthcare system than drinking and drug use, and like alcohol/drugs it is down the responsibility of the individual.
The other issue is that it's nearly impossible to prove an illness/disease was caused by 1 specific activity. Lung cancer rates are much higher among smokers, but when you get down to the individual level it's very hard to prove (a certain number of people were going to get lung cancer anyway).
You also have to decide how much is too much (or a zero tolerance policy). If someone smoked a couple cigarettes when they were 16 should they be denied healthcare for the rest of their life? If that's the case there is virtually no one who would be eligible for healthcare.
How about someone who smoked for a couple months? A couple years? How about someone who smoked a couple cigarettes a year for their whole life (at new years or whatever)?