This made me think of Michael Moore's documentary Bowling for Columbine and the "climate of fear" that the media has constructed in American society. Moore criticizes news media for populating daily life with stories of violence, tragedy, and fear that leads to an illusion of danger and need for self-defensive methods that ultimately allow more weapon access and more crime. At first glance, Berelson seems to say that these news stories are "non-serious" as in, they're not important or worth reporting on. Taking Moore's perspective, it could also be that they're not AS serious as they're made out to be and are flooding the reader attention for news that may be bigger than a single murder: genocide, tyranny, torture, etc. There are issues that need people to take part in and rise to action to change circumstances that would other worsen - action and attention is useless to small-time murder cases.
From what I gathered in this investigation, it's almost as if the newspaper is not the "source of information on political affairs" that people has permanently defined it in their heads. Rather, it's more of an entertainment source with comics and gossip columns and violent, action-filled, and emotion-driving stories with useful tools like movie guides and weather forecasts. Are journalists really reporting on what's important?
To lighten the mood a bit, here's a really beautiful song by one of my favorite bands - Boyce Avenue - that's a direct response to this "climate of fear". The beginning of the music video is even a montage of these types of news clips.