The MPAA is under pressure to make any movie containing smoking carry an R rating.
Ultimately, it's not really censorship, as theater chains decide what they will exhibit, and papers decide what to advertise, but statistically it would affect pictures' abilities to make a profit. Still, it's eerily similar to Hays Office style crackdowns, harshly condemning pictures that don't conform to the Production Code. Isn't this why we go to movies in the first place? I enjoy seeing characters doing things I will never do and that I know I should not do. That is part of the fundamental enjoyment of cinema. I understand the desire to keep cigarettes away from children (or even the sexualized image of smoking), but this is punishing people who had nothing to do with the kids' own disgusting decision to start smoking. It reminds me of a certain crass Onion article.
Besides, when shot correctly, a contemplative curl of cigarette smoke can become a character of its own. This ruling would render Wong Kar Wai's films veritably pornographic.