I suspect this professor is one of those people with an axe to grind against Wikipedia and other resources for not being trustworthy enough. Problem is, these kind of tactics would apply to old-fashioned print publications just as well. In the end it all comes down to a matter of trust: the reader has to trust a publication, the publisher has to trust an author, &c. Teaching people to violate that trust can only do harm. His exercises are probably more exciting and sensational this way, but if you ask me it would be more constructive & useful if he asked students to track down and correct surprising inaccuracies for example.