[jpadkins]

One reasoning flaw I've seen in this type of discussion is the assumption that the person has the same value system as you / the experts. In your example, it is assumed that the subject values a very long life. Maybe they don't, maybe they value smoking way more than a long life.

I largely agree with you, but I would tweak it to say "Humans are decent at doing what's best for them given their own values and knowledge".