"Semantic Stopsigns" are an interesting way to look at such ideas. I normally thought of "God!" as a disclaimer, or like the MPAA rating you see just before a movie starts: it told me before I continued into conversation with that person, that that person had limitations to their intellectual capacity or intellectual honesty. But I think "stop sign" is a better, nicer metaphor because it doesn't necessarily imply cognitive limitations. While someone who is incapable of thinking beyond "God!" would stop at this stopsign, so might a person who needed to look at a map for a moment (e.g., someone gathering their thoughts, or deciding whether such a debate would be enjoyable).
I also found it interesting that the author claimed that "intelligence" used to be one of his own semantic stopsigns. I'm not sure I understand what that means. "What makes you so sure you're right? Intelligence!" So the fact that someone is capable of thinking rationally means that they are right about them being able to think rationally and thus be right? Beyond that stopsign might be the questions "what is 'right?'" or "are there other means to being right?"