Answer :

The way they were raised:most of our beliefs come from our parents growing up they give us most of our preferences good or bad. the other one I have is history: I only say this one as I have met someone who was racially prejudiced because of her history with them.  
0rae0
people are raised a certain way, for instance, everyone is taught that 2 + 2 = 4, so you probably wouldn't believe someone if they told you 2+2=5, would you? they are, out of habit, against something with out much reason except its all they know. Also, some people's religious beliefs say that the white race is a superior race (although only ever males). just saying, my opinion is if you are racially prejudiced, you are not a very open or kind person.