You can level that criticism at an source of information. Do you think that any American textbook is going to give a flattering account of the British side of the story leading up to their declaration of independence. Heck no. But that doesn't mean that either side of the story fails to exist. It just means that you find it in different places.
The Wikipedia is one place where those ideas have the potential to come together, and for people to discuss those varying ideas. Yes, you may personally lose out for whatever reason. No, that doesn't mean that they are wrong. But if you do lose out, at least someone can go through the history of the document to see where the debate over facts popped up. You cannot do that in a book. (It's also worth noting that just because you personally believe that something is true, that doesn't make it true.)
Another issue was brought up, and that is people using the Wikipedia as a first-stop and only-stop for information. That is not the fault of the Wikipedia. It is the fault of the researcher. I have heard the same criticism leveled at the CIA World Factbook. I have heard the same criticism leveled at encyclopedias. Heck, I've even heard the same criticism leveled at the web at large.
I think a big part of the reason for that is that online sources (and encyclopedias) are usually secondary sources and the dependence upon these sources is more of a sign of intellectual laziness. Not only do these sources do a lot of the interpretation for you, but they are also a one-stop source of anything you want. No thought required.
But that doesn't mean that the Wikipedia is bad. It just means that you should broaden your horizons. And I still standby what I said earlier on issues like peer review.