There seems to be some confusion about when questions will be closed as "not constructive" and whether debate over certain things (such as the validity of an answer) would qualify a question for closure as not constructive.
The full text when voting to close as "not constructive" is this:
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or specific expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, see the FAQ for guidance.
Voting for closure as "not constructive" happens, among other reasons, when a question is asking a question that doesn't have a single, verifiable correct answer (usually such questions are asking for opinions). If I was to ask "Is C++ better than Java?" then that's going to solicit debate; people who prefer Java are going to post that Java is better, people who prefer C++ are going to post that C++ is better. Then they're (probably) going to go back and forth in a (vain) attempt to prove to the other people that they're correct.
That debate may never happen. In fact the point of closing the question as "not constructive" is to prevent it from happening.
However, it's possible for debate about a question to happen without the question itself being considered "not constructive"; I've seen questions about certain aspects of web development trigger a debate about whether they'd be considered "front end" or "back end". I also regularly "debate" with other users about the validity of answers to questions. Neither of those debates have any bearing on whether the question itself is "not constructive", though.
To sum up: There isn't a useful metric to determine whether a debate is occurring, and debate doesn't necessarily mean that a question is "not constructive".