For years now, it has been given that anyone who cites "nazis" as part of an argument has lost and is clutching at straws.
Over the past couple of years the term "MSM" has come to occupy the same position. Anyone using this vague catch-all term is trying to give the impression that they have some kind of privileged information that can be gained only from specialist sources (Twitter, Facebook, niche forums etc.), unavailable to the unenlightened. It implies that others are too stupid or sheeplike to work out for themselves who's right and who's wrong.
A worthless and cliched attempt to show superiority when all else has failed.