What needs to be emphasized, because most people misunderstand it (evidence: all the comments around here): The problematic thing is _false_ balance, that is, making a show of representing both sides while actually doing a crappy job for one side. _Real_ balance is something to strive for. False balance might be equally bad or worse than just representing one side. But a properly balanced article is far preferrable to both. And the right approach to fixing false balance is not to remove one viewpoint, but to add arguments, evidence and (if nothing else is available) trustworthy opinions.

Also, balance doesn't mean that a reader will go away with a feeling of "this issue is 50-50, might as well throw a coin to decide". Balance in this case should mean that the writer has put a similar amount of effort into understanding and representing both sides. And if the writer happens to lean towards one side and naturally know more about it, that means making up for that inherent bias.