It's not just that Wikipedia is a secondary source. In most cases, Wikipedia only allows articles to cite other secondary sources. This has led to some instances where very obvious disinformation stays on Wikipedia just because nobody that Wikipedia considers credible is writing articles from a certain perspective.
One example I know of is disinformation in the opening section of the Gamergate harrassment campaign article. (DISCLAIMER: I do not support Gamergate.) The article describes certain claims as "false" and "conspiracy theories" even though those claims were mostly true (but not newsworthy). The primary sources from 2014 are still online, but Wikipedia strangely does not consider primary sources to be reliable, so instead the citations go to random bloggers.