Wikipedia, as an encyclopedia, aspires to be authoritative by definition. Including the opinions of "some people" in an encyclopedia article implicitly gives credibility to their opinion and vouches for its relevance, because if it weren't important or relevant, it wouldn't have been included. Given the unique nature and status of Wikipedia, this makes its articles troublingly easy to exploit in this way in order to spread hearsay, personal opinion and even propaganda. The first line of defense against this is verifiability policy, which provides specific criteria for the sort of support a claim must have to survive a challenge in article space.
As you read the core content policies you see how ironic it is that Wikipedia in one way doesn't contain any data. It is a collection of metadata with references to published data--effectively a huge database of links maintained by the public. How backward is that?