xkcd

As a middle ground kind of guy, I would like to pre-emptively state that a lot of us don't actually think the answer is always the middle ground between two stances. It's just that we're more likely to propose a middle ground solution because we evaluate the plausibility of both stances in a more balanced way (as opposed to existing-stance-holders who are prone to bias towards their own stance.) When the two seem roughly equal in plausibility (which happens fairly often, otherwise the argument would be more one-sided,) that's an indication to evaluate the middle ground as well.

Middle ground folks are often caricaturized as wanting to find the middle ground between an objectively sensible point A and a radically wrong point B, when the spectrum of opinions is sort of like [ - - - - - A - | - - - - - - B ]. In that caricature, we're looking for a middle ground at point C [ - - - - - A - | - - C - - - B ], when in actuality we're evaluating (and not automatically accepting) something two or three steps closer to A. In some such cases, A might already be the most sensible middle ground.