Why do certain parents not want their kids to be in an interracial relationship?

My mom recently just got remarried and before now their was never a real "issue" with whom my sister and i called, text messaged, spent time with, came over, or anything like that. well now that she is married and her husband is from mississippi its a HUGE!! deal because she thinks that my sister and i talk to people of differet races to bother her because my step dad iand his children arent really "racist" but they use the N word. which bothers me!! when your just refering to someone who is an African American. Is it realy wrong to date other races? Or is it just the fact that people aren't used to seening couples like this? It's really hard sometimes just to listen to my mom say.. "well.. i think that you are just doing this because you kow that it bothers me.".. but before it never fased her!! And if it is just the fact that people just aren't used to it yet.. will it ever get better?