First of all, it depends on the age of the kid. At some point you have to let them figure things out for themselves. You can guide, but you can't force. From what I saw when I was younger, most parents who tried to force things on their kids only succeeded in making them rebel harder.
My mother didn't freak when I was in the phase where I listened to bodycount and other groups with questionable lyrics.
She didn't freak when I was virtually always with my sensei instead of at home.
She didn't freak when I old her I'd do kickboxing during the summer holiday.
She didn't freak when I told her one late spring day that I didn't feel like going to school anymore that year (last year Masters Degree), but instead spent all my time simply studying at home.
She didn't freak when I came home early in the morning, with too much beer in my body, and then went to jiu-jitsu class to help teach the kids.
Instead she let me make my own choices, guided me on the way, was there for me whenever I needed her, and gave me advice when I needed it.
In the end, I turned out allright. Most kids are intelligent enough to make the right choices and learn things for themselves.
Btw I still like bodycount, rage against the machine, rammstein, and lots of other groups with sometimes questionable lyrics. just because it sounds great doesn't mean I agree with all the lyrics.