I always thought so but never had a good reasoning. The following diagram is an analytical representation of why relying on news sources for knowledge is bad.
If the happenings in the world is represented on a bell curve, the red circular areas above represent what the news sources will cover. Why? Because that portion is part of the outliers and thus provides the necessary spice that catches user attention and has some viral scope. The result is that the news sources provide a distorted world view that could be eons away from the actual.
This doesn't mean that news is not important or has no value. Just that its not a sound way of understanding your world.