The problem with (C) is that it doesn't point out the issue with Victor's response.
Victor doesn't need to provide examples of cases in which biased thinking has been detected and the source of that.
He is just pointing out that this has in fact happened, which must be the case if cases of of biased thinking have been detected.
The flaw here is that Victor is overlooking the possibility that the people who detected and identified the bias could have also been biased in some way. This is why (E) is the correct answer.
Hope that helps! Please let us know if you have any other questions.
