Let me back up a bit. Not everyone reading this probably participates in Twitter. It can be a terrifically useful tool for networking with colleagues, chatting with friends and promoting one's work. I use it for all three. But what it's not always very good for is a couple of little things like "context" and "nuance." It sucks for having an argument with someone. The very nature of the format--short little statements limited to 140 characters in length, which often appear with small delays and even out of chronological order sometimes--makes it quite a dicey proposition to use it for a multi-statement, back-and-forth exchange over a disagreement. It is really easy for two people who maybe aren't even that far apart in their viewpoint to suddenly flame up into an angry shouting situation. But the fully public nature of it is great when someone like me, who does not know either of these people, can observe something interesting.
I happened to see a tweet from the agent where she was passing along the info that another agent was open for submissions of YA fiction, but that writers should not bother to submit if their characters smoke. The agent concurred that smoking sucks and that she doesn't like to see it on TV shows either. OK, fine. That's the preference of this agent and at least one other. Personally, it doesn't worry me that much and I do not judge it as some kind of moral failing or menace to society and certainly would't reject a story based on that alone, but nor does it bother me that some agents and editors do have a problem with it. Well, later on, the writer that I mentioned above appeared to have engaged with the agent over this, making the case (in a way that the Twitter Effect probably made seem a lot more shrill than it really was from his perspective) that the fiction ought to be judged on its merits as fiction and not just on little failings of the characters. People in real life, after all, do things like smoke (and drink and have sex). It struck him as censorious that an agent or editor would ignore these realities and issue a blanket ban on smoking (and by extension, he seemed to think, other "vices," though those did not come up much in the Tweets that I read). What kind of head-in-the-sand person would be like that? seemed to be his position. This, of course (enhanced probably by the Twitter Effect), caused the agent to respond quite forcefully in defense of her position. Which was simply that all editors have preferences (obviously) and it would be dumb and incompetent for an agent or writer to submit a story with smoking in it to an editor who has made it clear that she doesn't like people smoking in novels. To the writer, the argument was about art and reality, and to the agent is was about business and good professional practices.
Well, they were both right in their own ways, and it appeared to me that the whole thing flared up obnoxiously because they were talking about different things. I wasn't able to keep following it for very long, and it's possible that they solved their dispute and made peace. I hope so. At the base of it, the agent was just pointing out that a writer or agent will have more success with an editor if her submission matches the particular editor's preference. That's as common as common sense can get. If I submitted my NaNo novel to the local conservative religious book publisher, it would be quickly rejected because it has nothing to do with their preferences. If a writer submitted to my zine an item of When Harry Met Sally fan fiction, I would turn that away, too, for the same reason, and I'd wonder why the writer sent it to me in the first place and probably think they were incompetent for having done so. Just as the religious publisher would think that of me if I sent them my story about gay people with a bunch of sex and drinking in it. I don't think the writer who was arguing with the agent would disagree with any of this if he had encountered it anywhere else other than the context/nuance-free zone that Twitter can be at its worst. But, on the other hand, I sympathize with his apparent attitude that it's kind of priggish and silly to evaluate writing and story on something like a character smoking. But if you are determined to have smoking in your story, I am sure there are plenty of places to send it still, and it would be simple good sense to avoid the venues that ban it (obviously this would be a very different issue if, say, the government banned smoking in books, but that's not what this was about).
And I now know of a couple fewer possible people to show my NaNo novel to should I ever polish it up for submission (it has some smoking in it).