(this post is for extra credit)
Firstly, the argument that all facts spring forth out of opinions seems strange. As I write this, it is a fact that a few seconds ago on my computer screen I read these words: "all facts are based on opinion" (but then again it is possible that Descartes' demon is playing tricks with me). This statement (that facts come from opinions) can be translated into the phrase: all (objective) facts are subjective. But this is a paradox because the purported argument is a universal fact.
Moving forward, a better argument in my opinion would be to say that the interpretation and presentation of facts can be (and very often are) subjective and founded on opinion. That is, the fact that water is H2O is an objective truth (or, if you object due to linguistic reasons, it is a truth that the object me exists), but how the mind interprets and presents this fact depends on the subject, not the water.
Concerning Wikipedia, I do think that many articles are biased to some degree. Some articles are flagged by Wikipedia administrators and regular editors alike as being too biased. Wikipedia makes a strong effort to ensure that its articles cite credible sources, that facts and sources are verifiable, and that articles are free from original research (which could be very biased indeed).
In brief, there are some articles on Wikipedia that contain material that is open to interpretation. For example, an article about a certain nation's political economy with the conclusion, "thus, free markets are necessary and best for a democratic and peaceful society" is certainly biased. However, Wikipedia makes an effort to suppress such assertive and bold statements, but the problem is that Wikipedia is always a step behind.
*I made this example up. Hopefully no such sentence is on Wikipedia.