The pop-up says that the site prefers questions which have an answer (or words to that effect). That sounds a bit more like mathematics. We are dealing with language here. It is a branch of the humanities we are discussing. Should they not thrive on argument and debate?
There is plenty of discussion here, but it is mostly confined to chat and to comments. As posts are structured in a question-and-answer format, and the answers ranked according to votes, it is simply not possible to use the software behind this site as a forum. Long comment chains also get trimmed or referred to chat when they veer off the topic of the question or answer to which they are attached.
The idea of having questions and answers instead of discussion is fundamental to the Stack Exchange model in general, not just EL&U:
[W]e bring together individual communities of experts on very specific topics.
We welcome questions that are clear and specific, representing real problems that you face; Stack Exchange is not the place for conversation, opinions, or socializing.
There are probably hundreds of other sites where discussion and debate about English are welcomed. There is nothing to prevent you from contributing there, or even promoting those sites over this one if you feel it is a superior model.