I will answer this question in two ways, because often people confuse the word affect and effect.
A negative 'affect' of the media's bias is the placement of blame, criticism, and biased commentary while trying to offer facts. This is a human tendency to correlate crime to socioeconomic status, and this is overall a form of "affect" that the media continues to spread out.
A negative "effect" of the media's bias is that it generalizes an idea, turns it into a "cliche", and then such idea becomes an expectation that the audience might take to, and will then continue to expand and let take over popular beliefs. If, for example, the media focuses on one specific gang, or group with the slightest desire to spread some tendency against that group, automatically everything surrounding that group (neighborhood, ethnic background, socioeconomical status) becomes mixed with the media, and might produce a tendency for biased thinking among the public. This is what leads to generalizations, and to creating stereotypes.