To take this meta-discussion a step further, I think this is the inevitable course of an argument where one group cares about X but not Y, and the other group cares about Y but not X. The two debaters won't have much to say to each other except "Let's talk about X", "No, let's talk about Y", etc. You can't have a structured debate unless both people care about the same thing and hold explicitly contrary views on it. But this is rarely the case in today's fragmented information landscape where different information sources emphasize different things.