I suppose you're right. I've never found any problem determining the content of a film ahead of time, though. Also, I've seen most of the movies you mentioned, and don't remember folks walking out of them, either. If they were duped, you'd think they'd leave at some point.
In the same years all of those films were distributed, there were also dozens and dozens of other films distributed. My point is that people should choose the films they see carefully. After all, it costs a pretty penny to take your family to a film, what with the cost of tickets, plus any goodies from the concession.
Just on economic terms, it's worth making sure you'll enjoy the movie, both on an entertainment and a moral basis, don't you think?
That's why I don't choose films from ads. I choose them after reading about them. These days, that's pretty easy, since there are dozens of sites reviewing films. I like IMDB.com.
Yes, they should choose films carefully and beware of R-rated movies. The only r-rated movie I've seen in years was the Passion. Even pg-13 has gone downhill with sex and violence.