My mother slapped me when she found out I listen to Heavy Metal?

We are a strong Christian family. I listen to stuff like Iron Maiden. I don't see how it's wrong, I'm not breaking the law or anything. I see it just as music and it's not real, like the Terminator isn't real, but my brother watched that and didn't get into trouble. How is music any different? And I don't see what's Christian about slapping people either. Do you think it was right or wrong for her to slap me for that? Thank you.