Wikipedia, as a whole, cannot be placed under 'this is a valid site' or 'this is a site that should be invalidated'.
If you're looking for information for a research on Pepsi and possible health effects, are you going to go to Pepsi's official website? No, because they don't post criticism of themselves and therefore have a biased opinion. Wikipedia on the other hand tries to maintain a neutral point of view, and would add that information, and add sources for verifibility. Do you want to know something else, the Pepsi corporation even tried editing it's Wikipedia entry and tried to remove info about criticism (source: wikiscanner), kindy makes you think, right?
I'll try to look at another example. If I wanted information on the latest CD by my favorite band, why would I waste my time on the official website that could potentially tell me nothing except that the album is coming out, when I could look on Wikipedia were there could be sources about the tracks, release date, album covers, list of songs, and any other information?
Essentially, the argument of it being 'should it be invalidated' is simply a hit-and-miss on Wikipedia. If you're researching a major corporation or something of siginifcant meaning (like the above two examples), then chances are the entry is going to have verifiable sources from independent entries on the internet, and that makes it trustworthy. If the article is a paragraph of information without any sources and only links to it's 'official site', then no, it shouldn't be trusted, and that should be invalidated.
As a whole, it shouldn't be judged in any way, it should be judged per entry.