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Q1: Why isn't there more criticism of Sarkeesian or her work?
A1: Wikipedia policy requires that all material be verifiable to reliable, published sources with a reputation for fact-checking and accuracy, and that special care is to be taken in any material on living people. Additionally, sources must be reliable for the topic at hand, and their viewpoints must be given appropriate weight in proportion to their prominence among all others. The article reflects the viewpoints represented in reliable sources. See the talk page archives for previous discussions on individual sources.
Q2: I found a YouTube video/blog entry/customer review/forum thread that presents criticism of Sarkeesian's work.
A2: Those kinds of self-published and/or user-generated sources do not comply with Wikipedia's standards for reliable sources. In particular, the biographies of living persons policy prohibits any self-published sources in articles on living people except for a few very specific cases. Including such sources would a) tarnish the quality of Wikipedia's information and b) potentially open up Wikipedia to legal action.
Q3: I think I may have found a new reliable source that presents a viewpoint not yet covered in the article(s).
A3: You are welcome to bring any source up for discussion on the talk page, and the community will determine whether and how it may be included. However, first check the talk page archives to see if it has been discussed before.