SO isn't oriented around debate but around solving specific problems. I've asked many questions whose answers I needed. I've often gotten answers but not always. In this sense, "threads" or debates on some external issue are already a fail for SO's intent. I'm sure they're there but they're the exception.

Also - it takes 0 karma to answer a question and you get unlimited space. It takes 50 karma to leave a comment and you get about 200 words. If you've got lots of knowledge, you should have answered the question rather than tried to leave a comment on someone else's answer.