"They also like to reference the articles and books of other notables, as support either for their own position or to list alternative explanations that they think worthy of consideration."
References to others is meant to be a first link from the opinion presented to the facts supporting it, for those curious enough to want to learn more. It's hard to have firsthand knowledge of all relevant facts, so you have to learn through intermediaries, such as journalists, bloggers, analysts, and so on who in turn get their facts from more direct sources, who in turn get theirs more directly, until you can trace them to the source. Not all chains of facts are complete (occasionally something gets misinterpreted or fabricated), so it's sometimes worthwhile following a some of them to verify them.
Secondarily, references give you an indication of someone's preferences. Someone who refers often to Micheal Moore will have a certain interpretation of the same facts which differs from someone who refers to Bill O'Reily.
Giving an opinion without any references leaves that opinion fairly unsupported, making it no more reliable on its face than any other assertion (e.g. Kennedy was assasinated by squirrels). Although the "squirrel theory" might hold up after doing some independent investigation, if the squirrel theorist doesn't see fit to bother with any supporting evidence, why should anyone else bother treating it as more than ignorant speculation?