My daughter is autistic, if you knew the number of people, upon finding this out will come to me with "wonderful advice" from a TV show, movie, news article, etc. that they read, which, appears to make them experts on the subject.
Between that and the "OH, what's her magical talent!" because somehow, all autistic people is a savant/genius because of the movies, TV show, news articles, etc.
And then there's the "I have a friend whose got an autistic cousin, so I know all about it!".
I look at it with the mentality that people either just simply want to be useful and think that you might not know about something (and that's ok), or have pronounced themselves experts (and they can jump in a lake).
I will admit that I will offer "free advice" on some things, but on subjects that I actually have a LOT of experience and knowledge about it, not from TV shows, movies, news article, etc. But I usually see that the person tends to believes that they already know all about it (even though the reason why I would speak up would be exactly because they are doing something stupid). So I tend to really hold back and live and let live, say a little thing and see the reaction, or put it as a question instead. Their attitude tells me to either convey the info, or let them learn on their own.
So for those people as your comment, I'd simply go with "Ah, I see your swallowed the kool-aid... btw, all those bad things you heard, it's all made up stuff by pharmaceuticals and governments because of all the money they are losing with the people that are quitting smoking, care to learn more?".