When parents impose their customs..

Prejudice it's a very ugly thing to have. Prejudice is the feeling of rebelian towards another person of a diferent race or diferent culture, like jewish people used to be discriminated because they weren't catholics and they even were sent to work camps, but now it's more against homossexuals, transexuals or black people, although that's starting to vanish.
For instance, a father of three is against black people, what he does is to try to input those wrong thoughts in his children's mind, in order to make them dislike the things he dislike.
If we think hard enough we realise that most of the things we like or dislike are aquired based on what our parents, or big brothers, teach us, of course when we are old enough to think for our selfs we are able to make our own choises, but most of those choises are a little bit influenced on what our parents used to say to us when we were little. Parents transmite to us values for a person's caracter and personality, but they can also transmite bad things such as prejudice towards something or someone and, when we have that prejudice, we tend to discriminate those people and try to make our friends and loved ones feel the way we feel about that especific thing.
Of course we can always change our way of thinking any time of our lives, but sometimes we can be just a little to late.