I haven't really thought about whether I would be a business partner with someone, but in this case quantity certainly matters. When people say smoker, it is implied someone who smokes often and constantly throughout the day - 24/7. The equivalent drinker would be an alcoholic, not just someone who has a beer on Friday.
2) alcoholism has much worse direct consequences than heavy smoking
Being overweight is a different card, because it's a symptom, not an action that is chosen voluntarily. There can be many reasons for being overweight... maybe genes, some kind of illness etc.. I can't judge based on something I don't exactly know. But then again ... when I see someone eating lots of fast-food, chips and drinking Cola ... I would probably hesitate to ask him to become my business partner.