A seemingly common criticism of the media is that its coverage isn't balanced. This begs the question - what would truly balanced coverage look like?
Discussing the positive aspects of an issue 50% of the time and the negative aspects of an issue the other 50% isn't necessarily balanced, after all. Car crashes are a good example of this. When they're discussed in the news, 50% of the alloted talk time isn't dedicated to how the world has benefited from them.
So what would truly balanced coverage of (as an example) the Iraq war look like? If it isn't 50/50, what would it be? And, of course, how would we even recognize it when we saw it? Just because something "feels" balanced, doesn't necessarily mean that it is.
This is an excellent and hard question. Balanced coverage is a problem in science journalism, since there sometimes is a tendency to go for a 50/50 approach, even if one side of the debate is much better supported by the scientific evidence than the other. In that case 50/50 seems clearly unbalanced, and it looks like one might be able to come up with some principle of balance in terms of the weight of evidence or the weight of opinion in the qualified professional community. Of course this won't be easy to work in practice, but at least there are some principles one might have. In the case of political balance, the situation is much more difficult: difficult to work out what 'balance' means and, as you say, difficult to see how we could recognize balance and imbalance, even if we knew in the abstract what they mean.