What is one key theoretical contribution to our understanding of race, class, gender and sexual orientation ideologies in the media?
The umbrella under which preconceived notions and expectations of specific social groups are created is Social Identity (SI) theory, as proposed by Henri Tajfel in 1979.
Tajfel's proposal essentially states that we all have a need to belong to the social world. As such, we identify with the unique traits of the group that we belong to, labeling ourselves with identity symbols that may range from the sublime to the flamboyant. This is yet another concept in Psychology known as "Symbolic Interactionism," and it was proposed by Strayer (1980).
On the other hand, SI tells us we also tend to observe and criticize people in other groups. The other groups are observed especially if they pose a threat to or are in competition with us. This criticism does not have to be negative at all times; some groups mimic behaviors of other groups to gain social advantage. As such, we tend to award traits and characteristics to all groups in general, as we witness their differences and similarities to us, i.e: the Brits are this, Americans are that, etc.
Therefore, yes, it is a common tendency in humans to associate, categorize, label, judge, rate, and "package" other people based on the physical and behavioral traits that make them stand out.
This being said, the media does the same thing. In fact, the media takes advantage of the identifying factors of race, gender and culture, and propels them through embellishment for entertainment purposes. The problem is that, in recent years, our society has developed a higher degree of social and cultural sensitivity and some groups have argued that these embellishments touch upon racism.
However, what many people in the field are doing these days is playing it safe by openly admitting that they will push buttons, create drama, or be politically incorrect, on purpose. This is how movies that could be otherwise considered racist or mocking, such as Django Unchained, the Scary Movie franchise, and even the Medea films, are actually quite successful. It is not that they are funny in that they mock defining qualities in others, but in that they acknowledge that they do this precisely because it is a human tendency that we often negate but, in the right forums, could result in a curious and even funny experience.