I can easily tell my classmate that I used to have an old friend but now we're enemies because that old friend is a backstabbing scum of the earth and then I can enumerate the number of ways that old friend betrayed me. My classmate, the person I was talking to, will probably remember this and believe me because I said it in such a believable way and when my classmate sees my now sworn enemy, my classmate is sure to have some opinion about my old friend already because she/he has heard about my old friend from me - it doesn't even matter that my old friend never did anything to my classmate or if they've never met each other before; there will already be some sort of bias in my classmate's mind.
Now imagine this on the TV, the movies you watch, the books you read, and the articles you see on the internet, change the situation to some other issue, and multiply your classmate, your audience, by several billion.
If a certain show portrays a group of people to be inherently bad people, and they gave some believable evidences, you will probably think of that group of people as bad people too; it doesn't matter if you've met them before or if you'll ever meet them, what matters is you've seen some believable situations on your screens that seem real to you. If several books you've read says that if a person acts a certain way then she/he definitely falls into a stereotype, you will probably believe that because several books already said so. How people, things, culture, and everything else are represented in mass media greatly affects how everyone else sees these things. It does not matter if they have experienced it themselves - they will already have some preconceived opinion about it.
How media represents things is very crucial to how everyone else in the world sees things and that is why media representation is very important. From the things we perceive as normal to the things we find weird, all of that is influenced by what we see around us and on our screens. Everything you see is a representation of what other people think is right and what other people see as acceptable. In this time and age when our lives are being taken over by mass media without us being fully aware of it, we have to learn how to think for ourselves. We have to learn to dissect the things we see and analyze what is being served to us on TV before we believe them.
Don't let yourselves be fooled into thinking that everyone who looks like the bad person on your TV screen is bad. Don't allow yourselves to believe that you have to look a certain way because your magazines and books says it's more acceptable. Don't let yourselves limit other people just because of what they look like. Everyone and everything is more than how they are perceived on your screens.
Learn how to think for yourselves and analyze what is being served to you by the media.